Loops

while loop

The syntax of the while loop is-

while(expression)
{
    // statements
}

In the while loop, first, expression is evaluated. If the expression is true, then and only then the body of a loop is executed. After the execution of the body of the loop, again expression is evaluated, and if it is found to be true again, then the body of a loop is executed. This means that the body of a loop is executed continuously till the expression is true. Once the expression becomes false, the loop terminates, and the control goes out of the loop.

Flow diagram

Example 

// C program to illustrate while loop
#include<stdio.h>
int main()
{
    int i=0;    // initializing the variable
    while (i<5)    // while loop with condition
    {
        printf("Coding Ninjas\n");
        i++;    // incrementing operation
    }
    return 0;
}

You can also try this code with Online C Compiler

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Output

Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas

do-while loop

The syntax of the do-while loop is-

do
{
  // statements
}while(expression);

In the do-while loop, first, the body of a loop is executed, and then the expression is evaluated. If the expression is true, then again, the loop's body is executed, and this process continues until the expression is true. When the expression becomes false, the loop terminates. In the while loop, the loop's body is executed only when the expression is true, whereas, in the do-while loop, the loop's body will be executed at least once, even if the expression is false.

Flow diagram

Example

// C program to illustrate do-while loop
#include<stdio.h>
int main()
{
    	int i=0; //initializing the variable
	do // do-while loop 
	{
    	printf("Coding Ninjas\n");
    	i++; // incrementing operation
	}while(i<5);
	return 0;
}

You can also try this code with Online C Compiler

Run Code

Output

Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas

You can also read about the jump statement, Tribonacci Series

for loop

The syntax of the for loop is-

for(expr1; expr2; expr3)
{
  // statements
}

In the above syntax, expr1 is an initialization expression, expr2 is a test expression or condition, and expr3 is an update expression. Firstly initialization expression is executed, and the loop variables are initialized, then the test expression is checked. Suppose the test expression(expr2) is true. In that case, the loop's body is executed. after executing the loop's body, control transfers to the update expression(expr3), it modifies the loop variables, and then again, the test expression(expr2) is checked. If the test expression(expr2) is true, the loop's body is executed again. This process continues till the test expression is true, and When the test expression becomes false, the loop terminates.

Flow diagram

Example 

// C program to illustrate do-while loop
#include<stdio.h>
int main()
{
    int i;
	for(i=0;i<5;i++) // for loop 
	{
    	printf("Coding Ninjas\n");
	}
	return 0;
}

You can also try this code with Online C Compiler

Run Code

Output

Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas
Coding Ninjas

Also read,  Short int in C Programming

Frequently asked questions

1. What is an infinite loop in C?
   Ans: An infinite loop is a loop that repeats indefinitely and does not terminate. An infinite loop is also called an indefinite loop or an endless loop.
    
2. What is the syntax for running two variables for loop simultaneously?
   Ans: Syntax:
   for (initialization_expr1, initialization_expr1; test_expr1, test_expr2; update_expr1, update_expr2)
   {
        // statements 
   }
    
3. What is for loop in C?
   Ans: The for loop in C language is a repetition control structure that allows you to efficiently write a loop that is executed a specific number of times.

Key takeaways

In this blog, We learned about loops, types of loops, and how these loops work with the help of flow diagrams.

Recommended Readings:

• Ternary Operator in C
• What are Loops in Java
   

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