How to use while loop in C / C++

In last tutorial, we discussed for loop and examples with for loop in C / C++. In this tutorial, we will learn about while loop in C / C++ and its working with the help of some examples.

The while loop is used a lot in programming languages, especially C and C++ languages. So let's see the syntax and how to use it.

Syntax of while loop in C / C++

The while loop will repeat an action without knowing the number of iterations in advance. It just iterates until a stop condition is met or a break, continue, ... statement is encountered.

Syntax of while loop

while(condition)
{
   statement(s);
}

Here,

• condition: This is the condition to continue the loop, there are two cases.
  • If true: Continue loop execution.
  • If false: Exit the loop.
• statement: The statements inside the loop body will be executed if the condition is true.

The while loop can also be represented by a for loop as follows:

for(;condition;) {
      statement(s);
}

For example: Suppose we want to display "Welcome to learnnc.com" 10 times, then the while loop would look like this:

int i = 1;
while(i<=10){
    cout<<"Welcome to learnnc.com\n";
    i++;
}

Flowchart of while loop in C / C++

How while loop in C / C++ work?

In the while loop, the condition of the loop will be considered first. If the condition is true then the statements inside the loop will be executed. This will repeat until the condition is false or encounters statements like break, continue, ... . Otherwise, if the condition is false then exit the loop.

*Note:

A very important point when using while loop is the stop condition of the loop. We need to have increment or decrement statements inside the while loop so that the loop variable changes through each iteration. This way we can end the execution of while loop otherwise the loop would execute indefinitely.

Infinite while loop in C / C++

Why is there this case? Because, when the condition of the loop is always true, the statements inside the loop are executed. This leads to infinite looping and no stopping.

An example of infinite while loop:

#include <iostream>  
using namespace std;  
     
int main () { 
    int i;
    while(i=1) {
       cout << "Infinite while loop!!!\n" << endl;
    } 
    return 0;
}

Explain:

This is the condition of the loop i = 1. There is no statement inside the loop that changes the value of i, so i = 1 is always true. This results in the statements inside the loop being looped indefinitely.

Output:

Difference between for and while loop in C / C++

The difference between for loop and while loop is shown in the following table:

While loop in C / C++ with examples

Here, we have two examples with while loop in C / C++. These are basic examples when using while loop in C/C++.

Example 1: Displays numbers from 1 to n, with n being entered from the user.

C++ programming:

#include <iostream>
using namespace std;
int main() {
  int n, i = 0;
  cout<<"Enter number n: ";
  cin>>n;
  cout<<"Numbers from 1 to "<<n<<" : \n";
  while(i<=n){
    cout<<i<<" ";
    i++;
  }
  cout<<"\n-------------------------------\n";
  cout<<"This program is posted at learnnc.com";
  return 0;
}

C programming:

#include <stdio.h>
 
int main(void) {
  int n, i = 0;
  printf("Enter number n: ");
  scanf("%d", &n);
  printf("Numbers from 1 to %d : \n",n);
  while(i<=n){
    printf("%d ",i);
    i++;
  }
   
  printf("\n-------------------------------\n");
  printf("This program is posted at learnnc.com");
  return 0;
}

Output:

Example 2: Displaying "Welcome to learnnc.com" n times, with n being entered from the user.

C++ programming:

#include <iostream>
using namespace std;
int main() {
  int n, i = 0;
  cout<<"Enter number n: ";
  cin>>n;
  while(i<=n){
    cout<<"Welcome to learnnc.com!!!\n";
    i++;
  }
  cout<<"\n-------------------------------\n";
  cout<<"This program is posted at learnnc.com";
  return 0;
}

C programming:

#include <stdio.h>
 
int main(void) {
  int n, i = 0;
  printf("Enter number n: ");
  scanf("%d", &n);
  printf("Numbers from 1 to %d : \n",n);
  while(i<=n){
    printf("Welcome to learnnc.com!!!\n");
    i++;
  }
   
  printf("\n-------------------------------\n");
  printf("This program is posted at learnnc.com");
  return 0;
}

Output:

In the next tutorial, we will learn about the do...while loop in C / C ++, please keep an eye on it. Thank youuuu !!!