c while assignment

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7 Assignment Expressions

As a general concept in programming, an assignment is a construct that stores a new value into a place where values can be stored—for instance, in a variable. Such places are called lvalues (see Lvalues ) because they are locations that hold a value.

An assignment in C is an expression because it has a value; we call it an assignment expression . A simple assignment looks like

We say it assigns the value of the expression value-to-store to the location lvalue , or that it stores value-to-store there. You can think of the “l” in “lvalue” as standing for “left,” since that’s what you put on the left side of the assignment operator.

However, that’s not the only way to use an lvalue, and not all lvalues can be assigned to. To use the lvalue in the left side of an assignment, it has to be modifiable . In C, that means it was not declared with the type qualifier const (see const ).

The value of the assignment expression is that of lvalue after the new value is stored in it. This means you can use an assignment inside other expressions. Assignment operators are right-associative so that

is equivalent to

This is the only useful way for them to associate; the other way,

would be invalid since an assignment expression such as x = y is not valid as an lvalue.

Warning: Write parentheses around an assignment if you nest it inside another expression, unless that is a conditional expression, or comma-separated series, or another assignment.

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7.5: While Loop

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Introduction to while Loops

There are two commonly used loops where the condition is tested before entering loop. These loops have the posibility of NEVER entering the body of the loop, depending on the condition. They are: while loop and for loop. This lesson covers the: while.

Understanding Iteration in General - while

The concept of iteration is connected to possibly wanting to repeat an action. Like all control structures we ask a question to control the execution of the loop. The term loop comes from the circular looping motion that occurs when using flowcharting. The basic form of the while loop is as follows:

In almost all languages the condition is a Boolean expression . The Boolean data type has two values – true and false. Let's rewrite the structure to consider this:

Within the while control structure there are four attributes to a properly working loop. They are:

• Initializing the flag -  this is important , with while loops you must initialize the flag (some people call this  priming the loop ).
• Test expression
• Action or actions
• Update of the flag -  this also is important  - if we never update the flag we have no way to exit the loop.

The initialization of the flag is not technically part of the control structure, but a necessary item to occur before the loop is started. The English phrasing is, "While the expression is true, do the following actions". This is looping on the true. When the test expression is false, you stop the loop and go on with the next item in the program. Notice, because this is a test before loop the action might not happen . It is called a test before loop because the test comes before the action. It is also sometimes called a pre-test loop, meaning the test is pre (or Latin for before) the action and update.

Human Example of the while Loop

Consider the following one-way conversation from a mother to her child.

Child: The child says nothing, but mother knows the child had Cheerios for breakfast and history tells us that the child most likely spilled some Cheerios on the floor.

Mother says: "While it is true that you see (As long as you can see) a Cheerio on floor, pick it up and put it in the garbage."

Note: All of the elements are present to determine the action (or flow) that the child will be doing (in this case repeating). Because the question (can you see a Cheerios) has only two possible answers (true or false) the action will continue while there are Cheerios on the floor. Either the child 1) never picks up a Cheerio because they never spilled any or 2) picks up a Cheerio and keeps picking up Cheerios one at a time while he can see a Cheerio on the floor (that is until they are all picked up).

The while Structure within C++

The syntax for the while control structure within the C++ programming language is:

The test expression is within the parentheses, but this is not a function call. The parentheses are part of the control structure. Additionally, there is not a semicolon after the parenthesis following the expression.

The four attributes of a test before loop are present. The initialization of the flag. The test is the equality relational comparison of the value in the flag variable to the lower case character of y. The action part consists of the 6 lines that prompt for data and then displays the total of the two ages. The update of the flag is the displaying the question and getting the answer for the variable loop_response.

This type of loop control is called an event controlled loop. The flag updating is an event where someone decides if they want the loop to execute again.

Using indentation with the alignment of the loop actions and flag update is normal industry practice within the C++ community.

Infinite Loops

At this point it's worth mentioning that good programming always provides for a method to insure that the loop question will eventually be false so that the loop will stop executing and the program continues with the next line of code. However, if this does not happen then the program is in an infinite loop. Infinite loops are a bad thing. Consider the following code:

The programmer assigned a value to the flag before the loop which is correct. However, he forgot to update the flag. Every time the test expression is asked it will always be true. Thus, an infinite loop because the programmer did not provide a way to exit the loop (he forgot to update the flag). Consider the following code:

No matter what the user replies during the flag update, the test expression does not do a relational comparison but does an assignment. It assigns 'y' to the variable and asks if 'y' is true? Since all non-zero values are treated as representing true within the Boolean concepts of the C++ programming language, the answer to the test expression is true. Viola, you have an infinite loop.

The undesirable semi-colon on the end of while line causes the action of the while loop to be the "nothingness" between the closing parenthesis and the semi-colon. The program will infinitely loop because there is no action (that is no action and no update). If this is the first item in your program it will appear to start but there will be no output.

Counting Loops

The examples above are for an event controlled loop. The flag updating is an event where someone decides if they want the loop to execute again. Often the initialization sets the flag so that the loop will execute at least once.

Another common usage of the while loop is as a counting loop. Consider:

The variable counter is said to be controlling the loop. It is set to zero (called initialization) before entering the while loop structure and as long as it is less than 5 (five); the loop action will be executed. But part of the loop action uses the increment operator to increase counter's value by one. After executing the loop five times (once for counter's values of: 0, 1, 2, 3 and 4) the expression will be false and the next line of code in the program will execute. A counting loop is designed to execute the action (which could be more than one statement) a set of given number of times. In our example, the message is displayed five times on the monitor. It is accomplished my making sure all four attributes of the while control structure are present and working properly. The attributes are:

• Initializing the flag
• Update of the flag

Missing an attribute might cause an infinite loop or give undesired results (does not work properly).

Missing the flag update usually causes an infinite loop.

Variations on Counting

In the following example, the integer variable age is said to be controlling the loop (that is the flag). We can assume that age has a value provided earlier in the program. Because the while structure is a test before loop; it is possible that the person’s age is 0 (zero) and the first time we test the expression it will be false and the action part of the loop would never be executed.

Consider the following variation assuming that age and counter are both integer data type and that age has a value:

This loop is a counting loop similar to our first counting loop example. The only difference is instead of using a literal constant (in other words 5) in our expression, we used the variable age (and thus the value stored in age) to determine how many times to execute the loop. However, unlike our first counting loop example which will always execute exactly 5 times; it is possible that the person’s age is 0 (zero) and the first time we test the expression it will be false and the action part of the loop would never be executed.

Definitions

 Adapted from: "While Loop"  by  Kenneth Busbee , Download for free at http://cnx.org/contents/[email protected]  is licensed under  CC BY 4.0

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In programming, loops are used to repeat a block of code until a specified condition is met.

C programming has three types of loops.

do...while loop

In the previous tutorial, we learned about for loop. In this tutorial, we will learn about while and do..while loop.

The syntax of the while loop is:

How while loop works?

• The while loop evaluates the testExpression inside the parentheses () .
• If  testExpression is true , statements inside the body of while loop are executed. Then, testExpression is evaluated again.
• The process goes on until testExpression is evaluated to false .
• If  testExpression is false , the loop terminates (ends).

To learn more about test expressions (when  testExpression is evaluated to true and false ), check out relational and logical operators .

Flowchart of while loop

Example 1: while loop

Here, we have initialized i to 1.

• When i = 1 , the test expression i <= 5 is true . Hence, the body of the while loop is executed. This prints 1 on the screen and the value of i is increased to 2 .
• Now, i = 2 , the test expression i <= 5 is again true . The body of the while loop is executed again. This prints 2 on the screen and the value of i is increased to 3 .
• This process goes on until i becomes 6. Then, the test expression i <= 5 will be false and the loop terminates.

The do..while loop is similar to the while loop with one important difference. The body of do...while loop is executed at least once. Only then, the test expression is evaluated.

The syntax of the do...while loop is:

How do...while loop works?

• The body of do...while loop is executed once. Only then, the testExpression is evaluated.
• If testExpression is true , the body of the loop is executed again and testExpression is evaluated once more.
• This process goes on until testExpression becomes false .
• If testExpression is false , the loop ends.

Flowchart of do...while Loop

Example 2: do...while loop

Here, we have used a do...while loop to prompt the user to enter a number. The loop works as long as the input number is not 0 .

The  do...while loop executes at least once i.e. the first iteration runs without checking the condition. The condition is checked only after the first iteration has been executed.

So, if the first input is a non-zero number, that number is added to the sum variable and the loop continues to the next iteration. This process is repeated until the user enters  0 .

But if the first input is 0, there will be no second iteration of the loop and  sum  becomes 0.0 .

Outside the loop, we print the value of sum .

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• do...while Loop
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Loops are used to execute statements or block of statements repeatedly. For example, suppose we want to write a program to print "Hello" 5 times. One way to achieve this is to write the following statement 5 times.

But what if we want to print it 100 or 1000 times. Of course, writing the same statement 100 times or 1000 times would be insane. Using loops we can solve this kind of problem easily. C provides three types of loops.

• do while loop

The while loop #

Just like the if-else statement , the while loop starts with a condition. First, the condition is evaluated, if it is true then the statements in the body of the while are executed. After executing the body of the while loop, the condition is checked again, if it is still true then once again statements in the body of the while are executed. This process keeps repeating until the condition becomes false. Therefore, you must always include a statement which alters the value of the condition so that it ultimately becomes false at some point. Each execution of the loop body is known as iteration.

The following program uses while loop to prints all even numbers between 1 to 100 :

Expected Output:

How it works:

In line 5, we have declared a variable i and initialized it to 1 . First, the condition (i < 100) is checked, if it is true. Control is transferred inside the body of the while loop. Inside the body of the loop, if condition ( i % 2 == 0 ) is checked, if it is true then the statement inside the if block is executed. Then the value of i is incremented using expression i++ . As there are no more statements left to execute inside the body of the while loop, this completes the first iteration. Again the condition ( i < 100 ) is checked, if it is still true then once again the body of the loop is executed. This process repeats as long as the value of i is less than 100 . When i reaches 100 , the loop terminates and control comes out of the while loop.

Consider one more example:

The following program calculates the sum of digits of a number entered by the user.

Expected Output: 1st run:

Let's say the user entered 123 , then here are the steps to find the sum of digits.

1st iteration #

1st step: #.

Take out the last digit of 123 by evaluating 123 % 10 and store the result in the variable remainder .

2nd step: #

Add the number obtained in the last step to the variable sum .

3rd step: #

Now we don't need the last digit of 123 , so remove it by evaluating 123 / 10 .

2nd iteration #

3rd iteration #.

When n reaches 0 while condition becomes false and control comes out of the while loop. Hence the sum of digits of 123 is 6 .

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Assignment operators.

Assignment and compound assignment operators are binary operators that modify the variable to their left using the value to their right.

[ edit ] Simple assignment

The simple assignment operator expressions have the form

Assignment performs implicit conversion from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs .

Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The value category of the assignment operator is non-lvalue (so that expressions such as ( a = b ) = c are invalid).

rhs and lhs must satisfy one of the following:

• both lhs and rhs have compatible struct or union type, or..
• rhs must be implicitly convertible to lhs , which implies
• both lhs and rhs have arithmetic types , in which case lhs may be volatile -qualified or atomic (since C11)
• both lhs and rhs have pointer to compatible (ignoring qualifiers) types, or one of the pointers is a pointer to void, and the conversion would not add qualifiers to the pointed-to type. lhs may be volatile or restrict (since C99) -qualified or atomic (since C11) .
• lhs is a (possibly qualified or atomic (since C11) ) pointer and rhs is a null pointer constant such as NULL or a nullptr_t value (since C23)

[ edit ] Notes

If rhs and lhs overlap in memory (e.g. they are members of the same union), the behavior is undefined unless the overlap is exact and the types are compatible .

Although arrays are not assignable, an array wrapped in a struct is assignable to another object of the same (or compatible) struct type.

The side effect of updating lhs is sequenced after the value computations, but not the side effects of lhs and rhs themselves and the evaluations of the operands are, as usual, unsequenced relative to each other (so the expressions such as i = ++ i ; are undefined)

Assignment strips extra range and precision from floating-point expressions (see FLT_EVAL_METHOD ).

In C++, assignment operators are lvalue expressions, not so in C.

[ edit ] Compound assignment

The compound assignment operator expressions have the form

The expression lhs @= rhs is exactly the same as lhs = lhs @ ( rhs ) , except that lhs is evaluated only once.

[ edit ] References

• C17 standard (ISO/IEC 9899:2018):
• 6.5.16 Assignment operators (p: 72-73)
• C11 standard (ISO/IEC 9899:2011):
• 6.5.16 Assignment operators (p: 101-104)
• C99 standard (ISO/IEC 9899:1999):
• 6.5.16 Assignment operators (p: 91-93)
• C89/C90 standard (ISO/IEC 9899:1990):
• 3.3.16 Assignment operators

[ edit ] See Also

Operator precedence

[ edit ] See also

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Assignment Operators in C

In C language, the assignment operator stores a certain value in an already declared variable. A variable in C can be assigned the value in the form of a literal, another variable, or an expression.

The value to be assigned forms the right-hand operand, whereas the variable to be assigned should be the operand to the left of the " = " symbol, which is defined as a simple assignment operator in C.

In addition, C has several augmented assignment operators.

The following table lists the assignment operators supported by the C language −

Simple Assignment Operator (=)

The = operator is one of the most frequently used operators in C. As per the ANSI C standard, all the variables must be declared in the beginning. Variable declaration after the first processing statement is not allowed.

You can declare a variable to be assigned a value later in the code, or you can initialize it at the time of declaration.

You can use a literal, another variable, or an expression in the assignment statement.

Once a variable of a certain type is declared, it cannot be assigned a value of any other type. In such a case the C compiler reports a type mismatch error.

In C, the expressions that refer to a memory location are called "lvalue" expressions. A lvalue may appear as either the left-hand or right-hand side of an assignment.

On the other hand, the term rvalue refers to a data value that is stored at some address in memory. A rvalue is an expression that cannot have a value assigned to it which means an rvalue may appear on the right-hand side but not on the left-hand side of an assignment.

Variables are lvalues and so they may appear on the left-hand side of an assignment. Numeric literals are rvalues and so they may not be assigned and cannot appear on the left-hand side. Take a look at the following valid and invalid statements −

Augmented Assignment Operators

In addition to the = operator, C allows you to combine arithmetic and bitwise operators with the = symbol to form augmented or compound assignment operator. The augmented operators offer a convenient shortcut for combining arithmetic or bitwise operation with assignment.

For example, the expression "a += b" has the same effect of performing "a + b" first and then assigning the result back to the variable "a".

Run the code and check its output −

Similarly, the expression "a <<= b" has the same effect of performing "a << b" first and then assigning the result back to the variable "a".

Here is a C program that demonstrates the use of assignment operators in C −

When you compile and execute the above program, it will produce the following result −

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• Callbacks in C
• Nested functions in C
• Variadic functions in C
• _Noreturn function specifier in C
• Predefined Identifier __func__ in C
• C Library math.h Functions

C Arrays & Strings

• Properties of Array in C
• Multidimensional Arrays in C
• Initialization of Multidimensional Array in C
• Pass Array to Functions in C
• How to pass a 2D array as a parameter in C?
• What are the data types for which it is not possible to create an array?
• How to pass an array by value in C ?
• Strings in C
• Array of Strings in C
• What is the difference between single quoted and double quoted declaration of char array?
• C String Functions
• Pointer Arithmetics in C with Examples
• C - Pointer to Pointer (Double Pointer)
• Function Pointer in C
• How to declare a pointer to a function?
• Pointer to an Array | Array Pointer
• Difference between constant pointer, pointers to constant, and constant pointers to constants
• Pointer vs Array in C
• Dangling, Void , Null and Wild Pointers in C
• Near, Far and Huge Pointers in C
• restrict keyword in C

C User-Defined Data Types

• C Structures
• dot (.) Operator in C
• Structure Member Alignment, Padding and Data Packing
• Flexible Array Members in a structure in C
• Bit Fields in C
• Difference Between Structure and Union in C
• Anonymous Union and Structure in C
• Enumeration (or enum) in C

C Storage Classes

• Storage Classes in C
• extern Keyword in C
• Static Variables in C
• Initialization of static variables in C
• Static functions in C
• Understanding "volatile" qualifier in C | Set 2 (Examples)
• Understanding "register" keyword in C

C Memory Management

• Memory Layout of C Programs
• Dynamic Memory Allocation in C using malloc(), calloc(), free() and realloc()
• Difference Between malloc() and calloc() with Examples
• What is Memory Leak? How can we avoid?
• Dynamic Array in C
• How to dynamically allocate a 2D array in C?
• Dynamically Growing Array in C

C Preprocessor

• C Preprocessor Directives
• How a Preprocessor works in C?
• Header Files in C
• What’s difference between header files "stdio.h" and "stdlib.h" ?
• How to write your own header file in C?
• Macros and its types in C
• Interesting Facts about Macros and Preprocessors in C
• # and ## Operators in C
• How to print a variable name in C?
• Multiline macros in C
• Variable length arguments for Macros
• Branch prediction macros in GCC
• typedef versus #define in C
• Difference between #define and const in C?
• Basics of File Handling in C
• C fopen() function with Examples
• EOF, getc() and feof() in C
• fgets() and gets() in C language
• fseek() vs rewind() in C
• What is return type of getchar(), fgetc() and getc() ?
• Read/Write Structure From/to a File in C
• C Program to print contents of file
• C program to delete a file
• C Program to merge contents of two files into a third file
• What is the difference between printf, sprintf and fprintf?
• Difference between getc(), getchar(), getch() and getche()

Miscellaneous

• time.h header file in C with Examples
• Input-output system calls in C | Create, Open, Close, Read, Write
• Signals in C language
• Program error signals
• Socket Programming in C
• _Generics Keyword in C
• Multithreading in C
• C Programming Interview Questions (2024)
• Commonly Asked C Programming Interview Questions | Set 1
• Commonly Asked C Programming Interview Questions | Set 2
• Commonly Asked C Programming Interview Questions | Set 3

Assignment operators are used for assigning value to a variable. The left side operand of the assignment operator is a variable and right side operand of the assignment operator is a value. The value on the right side must be of the same data-type of the variable on the left side otherwise the compiler will raise an error.

Different types of assignment operators are shown below:

1. “=”: This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. Example:

2. “+=” : This operator is combination of ‘+’ and ‘=’ operators. This operator first adds the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a += 6) = 11.

3. “-=” This operator is combination of ‘-‘ and ‘=’ operators. This operator first subtracts the value on the right from the current value of the variable on left and then assigns the result to the variable on the left. Example:

If initially value stored in a is 8. Then (a -= 6) = 2.

4. “*=” This operator is combination of ‘*’ and ‘=’ operators. This operator first multiplies the current value of the variable on left to the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 5. Then (a *= 6) = 30.

5. “/=” This operator is combination of ‘/’ and ‘=’ operators. This operator first divides the current value of the variable on left by the value on the right and then assigns the result to the variable on the left. Example:

If initially value stored in a is 6. Then (a /= 2) = 3.

Below example illustrates the various Assignment Operators:

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C++ Tutorial

C++ functions, c++ classes, c++ reference, c++ examples, c++ while loop.

Loops can execute a block of code as long as a specified condition is reached.

Loops are handy because they save time, reduce errors, and they make code more readable.

The while loop loops through a block of code as long as a specified condition is true :

In the example below, the code in the loop will run, over and over again, as long as a variable ( i ) is less than 5:

Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!

C++ Exercises

Test yourself with exercises.

Print i as long as i is less than 6.

Start the Exercise

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Loop programming exercises and solutions in C

In programming, there exists situations when you need to repeat single or a group of statements till some condition is met. Such as – read all files of a directory, send mail to all employees one after another etc. These task in C programming is handled by looping statements .

Looping statement defines a set of repetitive statements. These statements are repeated with same or different parameters for a number of times. Looping statement is also known as iterative or repetitive statement .

C supports three looping statements.

• do…while loop

In this exercise we will practice lots of looping problems to get a strong grip on loop. This is most recommended C programming exercise for beginners.

Always feel free to drop your queries, suggestions, hugs or bugs down below in the comments section . I always look forward to hear from you.

Required knowledge

Basic C programming , Relational operators , Logical operators , If else , For loop

List of loop programming exercises

• Write a C program to print all natural numbers from 1 to n.  – using  while loop
• Write a C program to print all natural numbers in reverse (from n to 1) . – using  while loop
• Write a C program to print all alphabets from a to z.  – using  while loop
• Write a C program to print all even numbers between 1 to 100.  – using  while loop
• Write a C program to print all odd number between 1 to 100.
• Write a C program to find sum of all natural numbers between 1 to n.
• Write a C program to find sum of all even numbers between 1 to n .
• Write a C program to find sum of all odd numbers between 1 to n .
• Write a C program to print multiplication table of any number .
• Write a C program to count number of digits in a number .
• Write a C program to find first and last digit of a number .
• Write a C program to find sum of first and last digit of a number.
• Write a C program to swap first and last digits of a number .
• Write a C program to calculate sum of digits of a number .
• Write a C program to calculate product of digits of a number .
• Write a C program to enter a number and print its reverse .
• Write a C program to check whether a number is palindrome or not.
• Write a C program to find frequency of each digit in a given integer .
• Write a C program to enter a number and print it in words.
• Write a C program to print all ASCII character with their values .
• Write a C program to find power of a number using for loop .
• Write a C program to find all factors of a number .
• Write a C program to calculate factorial of a number .
• Write a C program to find HCF (GCD) of two numbers .
• Write a C program to find LCM of two numbers .
• Write a C program to check whether a number is Prime number or not.
• Write a C program to print all Prime numbers between 1 to n.
• Write a C program to find sum of all prime numbers between 1 to n .
• Write a C program to find all prime factors of a number .
• Write a C program to check whether a number is Armstrong number or not.
• Write a C program to print all Armstrong numbers between 1 to n.
• Write a C program to check whether a number is Perfect number or not .
• Write a C program to print all Perfect numbers between 1 to n .
• Write a C program to check whether a number is Strong number or not .
• Write a C program to print all Strong numbers between 1 to n .
• Write a C program to print Fibonacci series up to n terms .
• Write a C program to find one’s complement of a binary number .
• Write a C program to find two’s complement of a binary number .
• Write a C program to convert Binary to Octal number system .
• Write a C program to convert Binary to Decimal number system .
• Write a C program to convert Binary to Hexadecimal number system .
• Write a C program to convert Octal to Binary number system .
• Write a C program to convert Octal to Decimal number system .
• Write a C program to convert Octal to Hexadecimal number system .
• Write a C program to convert Decimal to Binary number system .
• Write a C program to convert Decimal to Octal number system .
• Write a C program to convert Decimal to Hexadecimal number system .
• Write a C program to convert Hexadecimal to Binary number system .
• Write a C program to convert Hexadecimal to Octal number system .
• Write a C program to convert Hexadecimal to Decimal number system .
• Write a C program to print Pascal triangle upto n rows .
• Star pattern programs – Write a C program to print the given star patterns.
• Number pattern programs – Write a C program to print the given number patterns .