(C Programming Tutorials)
C while and do…while Loop
In this tutorial, you will learn to create while and do…while loop in C programming with the help of examples.
C programming has three types of loops.
- for loop
- while loop
- do…while loop
In the previous tutorial, we learned about for
loop. In this tutorial, we will learn about while
and do..while
loop.
while loop
The syntax of the while
loop is:
while (testExpression)
{
// statements inside the body of the loop
}
How while loop works?
- The
while
loop evaluates the test expression inside the parenthesis()
. - If the test expression is true, statements inside the body of
while
loop are executed. Then, the test expression is evaluated again. - The process goes on until the test expression is evaluated to false.
- If the test expression is false, the loop terminates (ends).
To learn more about test expression (when the test expression is evaluated to true and false), check out relational and logical operators.
Flowchart of while loop
Example 1: while loop
// Print numbers from 1 to 5
#include <stdio.h>
int main(){
int i = 1;
while (i <= 5)
{
printf("%dn", i);
++i;
}
return 0;
}
Output
1 2 3 4 5
Here, we have initialized i to 1.
- When i is 1, the test expression
i <= 5
is true. Hence, the body of thewhile
loop is executed. This prints 1 on the screen and the value of i is increased to 2. - Now, i is 2, the test expression
i <= 5
is again true. The body of thewhile
loop is executed again. This prints 2 on the screen and the value ofi
is increased to 3. - This process goes on until i becomes 6. When i is 6, the test expression
i <= 5
will be false and the loop terminates.
do…while loop
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:
do
{
// statements inside the body of the loop
}
while (testExpression);
How do…while loop works?
- The body of do…while loop is executed once. Only then, the test expression is evaluated.
- If the test expression is true, the body of the loop is executed again and the test expression is evaluated.
- This process goes on until the test expression becomes false.
- If the test expression is false, the loop ends.
Flowchart of do…while Loop
Example 2: do…while loop
// Program to add numbers until the user enters zero
#include <stdio.h>
int main(){
double number, sum = 0;
// the body of the loop is executed at least once
do
{
printf("Enter a number: ");
scanf("%lf", &number);
sum += number;
}
while(number != 0.0);
printf("Sum = %.2lf",sum);
return 0;
}
Output
Enter a number: 1.5 Enter a number: 2.4 Enter a number: -3.4 Enter a number: 4.2 Enter a number: 0 Sum = 4.70
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