Understanding Do...While Loop in C++

Do...While Loop in C++: An Overview

Do...While Loop in C++

It is an exit-controlled loop. It prints the output at least once before checking the condition. Afterwards, the condition is checked and the execution of the loop begins.

Syntax

do{
//code to be executed
}while(testCondition);

• The body of the loop executes before checking the condition.
• If the testCondition is true, the loop body executes again.
• Again the testCondition is evaluated.
• The process repeats until the testCondition becomes false.

Example to demonstrate do...while loop in C++ Compiler

#include <iostream>
using namespace std;
int main() {
 int i = 0;
 do {
 cout << i + 1 << endl;
 i++;
 } while (i < 10);
 
 return 0;
}

• The above code prints numbers from 1 to 10 using the do...while loop in C++.
• It prints 1 before checking if i<10.
• It checks the condition i<10 and executes until i becomes 10

Output

1
2
3
4
5
6
7
8
9
10

Read More - C++ Interview Interview Questions and Answers

Nested Do...While Loop in C++

Example to demonstrate Nested do...while loop in C++

 #include <iostream>
using namespace std;
int main() {
 int i = 1;
 
 do {
 int j = 1;
 do {
 cout << i << " * " << j << " = " << i * j << endl;
 j++;
 } while (j <= 10);
 i++;
 } while (i <= 2);
 
 return 0;
}

• The above code creates and outputs multiplication tables of 1 and 2 from 1 to 10 using a nested loop structure.
• It iterates over the values of i (1 and 2) and j (1 to 10), outputting the result of i * j after each iteration using two nested do...while loops.

Output

1 * 1 = 1
1 * 2 = 2
1 * 3 = 3
1 * 4 = 4
1 * 5 = 5
1 * 6 = 6
1 * 7 = 7
1 * 8 = 8
1 * 9 = 9
1 * 10 = 10
2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20

Infinite do...while loop in C++

Syntax

do 
{ 
 // body of the loop 
}while(true);

Example to demonstrate infinite do...while loop in C++ Editor

 #include <iostream>
using namespace std;
int main() {
 do {
 cout << "This is an infinite do-while loop." << endl;
 } while (true);

 return 0; // This return statement may never be reached.
}

Output

This is an infinite do-while loop.
This is an infinite do-while loop.
This is an infinite do-while loop. 
...

Summary