When is it beneficial to use while loop and do-while loop in your program give an example of each

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C++ while Loop
Flowchart of while Loop
Example 1: Display Numbers from 1 to 5
Example 2: Sum of Positive Numbers Only
C++ do...while Loop
Flowchart of do...while Loop
Example 3: Display Numbers from 1 to 5
Example 4: Sum of Positive Numbers Only
Infinite while loop
for vs while loops

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while loop:

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as a repeating if statement.
Syntax :

while (boolean condition) { loop statements... }

Flowchart:

Example:

#include <stdio.h>
int main()
{
    int i = 5;
    while (i < 10) {
        printf("GFG\n");
        i++;
    }
    return 0;
}

#include <iostream>

using namespace std;

int main()

{

int i = 5;

while (i < 10) {

i++;

cout << "GFG\n";

}

return 0;

}

import java.io.*;
class GFG {
    public static void main(String[] args)
    {
        int i = 5;
        while (i < 10) {
            i++;
            System.out.println("GfG");
        }
    }
}

Output:GFG GFG GFG GFG GFG

do-while loop:

do while loop is similar to while loop with the only difference that it checks for the condition after executing the statements, and therefore is an example of Exit Control Loop.

Syntax:

do { statements.. } while (condition);

Flowchart:

Example:

#include <stdio.h>
int main()
{
    int i = 5;
    do {
        printf("GFG\n");
        i++;
    } while (i < 10);
    return 0;
}

#include <iostream>
using namespace std;
int main()
{
    int i = 5;
    do {
        i++;
        cout << "GFG\n";
    } while (i < 10);
    return 0;
}

import java.io.*;

class GFG {

public static void main(String[] args)

{

int i = 5;

do {

i++;

System.out.println("GfG");

} while (i < 10);

}

Output:GFG GFG GFG GFG GFG

Here is the difference table:

while	do-while
Condition is checked first then statement(s) is executed.	Statement(s) is executed atleast once, thereafter condition is checked.
It might occur statement(s) is executed zero times, If condition is false.	At least once the statement(s) is executed.
No semicolon at the end of while. while(condition)	Semicolon at the end of while. while(condition);
If there is a single statement, brackets are not required.	Brackets are always required.
Variable in condition is initialized before the execution of loop.	variable may be initialized before or within the loop.
while loop is entry controlled loop.	do-while loop is exit controlled loop.
while(condition) { statement(s); }	do { statement(s); } while(condition);

In computer programming, loops are used to repeat a block of code.

For example, let's say we want to show a message 100 times. Then instead of writing the print statement 100 times, we can use a loop.

That was just a simple example; we can achieve much more efficiency and sophistication in our programs by making effective use of loops.

There are 3 types of loops in C++.

for loop
while loop
do...while loop

In the previous tutorial, we learned about the C++ for loop. Here, we are going to learn about while and do...while loops.

C++ while Loop

The syntax of the while loop is:

while (condition) { // body of the loop }

Here,

A while loop evaluates the condition
If the condition evaluates to true, the code inside the while loop is executed.
The condition is evaluated again.
This process continues until the condition is false.
When the condition evaluates to false, the loop terminates.

To learn more about the conditions, visit C++ Relational and Logical Operators.

Flowchart of while Loop

Flowchart of C++ while loop

Example 1: Display Numbers from 1 to 5

// C++ Program to print numbers from 1 to 5 #include <iostream> using namespace std; int main() { int i = 1; // while loop from 1 to 5 while (i <= 5) { cout << i << " "; ++i; } return 0; }

Output

1 2 3 4 5

Here is how the program works.

Iteration	Variable	i <= 5	Action
1st	i = 1	true	1 is printed and i is increased to 2.
2nd	i = 2	true	2 is printed and i is increased to 3.
3rd	i = 3	true	3 is printed and i is increased to 4
4th	i = 4	true	4 is printed and i is increased to 5.
5th	i = 5	true	5 is printed and i is increased to 6.
6th	i = 6	false	The loop is terminated

Example 2: Sum of Positive Numbers Only

// program to find the sum of positive numbers // if the user enters a negative number, the loop ends // the negative number entered is not added to the sum #include <iostream> using namespace std; int main() { int number; int sum = 0; // take input from the user cout << "Enter a number: "; cin >> number; while (number >= 0) { // add all positive numbers sum += number; // take input again if the number is positive cout << "Enter a number: "; cin >> number; } // display the sum cout << "\nThe sum is " << sum << endl; return 0; }

Output

Enter a number: 6 Enter a number: 12 Enter a number: 7 Enter a number: 0 Enter a number: -2 The sum is 25

In this program, the user is prompted to enter a number, which is stored in the variable number.

In order to store the sum of the numbers, we declare a variable sum and initialize it to the value of 0.

The while loop continues until the user enters a negative number. During each iteration, the number entered by the user is added to the sum variable.

When the user enters a negative number, the loop terminates. Finally, the total sum is displayed.

C++ do...while Loop

The do...while loop is a variant of the while loop with one important difference: the body of do...while loop is executed once before the condition is checked.

Its syntax is:

do { // body of loop; } while (condition);

Here,

The body of the loop is executed at first. Then the condition is evaluated.
If the condition evaluates to true, the body of the loop inside the do statement is executed again.
The condition is evaluated once again.
If the condition evaluates to true, the body of the loop inside the do statement is executed again.
This process continues until the condition evaluates to false. Then the loop stops.

Flowchart of do...while Loop

Flowchart of C++ do...while loop

Example 3: Display Numbers from 1 to 5

// C++ Program to print numbers from 1 to 5 #include <iostream> using namespace std; int main() { int i = 1; // do...while loop from 1 to 5 do { cout << i << " "; ++i; } while (i <= 5); return 0; }

Output

1 2 3 4 5

Here is how the program works.

Iteration	Variable	i <= 5	Action
	i = 1	not checked	1 is printed and i is increased to 2
1st	i = 2	true	2 is printed and i is increased to 3
2nd	i = 3	true	3 is printed and i is increased to 4
3rd	i = 4	true	4 is printed and i is increased to 5
4th	i = 5	true	5 is printed and i is increased to 6
5th	i = 6	false	The loop is terminated

Example 4: Sum of Positive Numbers Only

// program to find the sum of positive numbers // If the user enters a negative number, the loop ends // the negative number entered is not added to the sum #include <iostream> using namespace std; int main() { int number = 0; int sum = 0; do { sum += number; // take input from the user cout << "Enter a number: "; cin >> number; } while (number >= 0); // display the sum cout << "\nThe sum is " << sum << endl; return 0; }

Output 1

Enter a number: 6 Enter a number: 12 Enter a number: 7 Enter a number: 0 Enter a number: -2 The sum is 25

Here, the do...while loop continues until the user enters a negative number. When the number is negative, the loop terminates; the negative number is not added to the sum variable.

Output 2

Enter a number: -6 The sum is 0.

The body of the do...while loop runs only once if the user enters a negative number.