The do-while loop is used to execute a block of code repeatedly while a specified condition is true. The main difference between a while loop and a do-while loop is that the do-while loop executes its body at least once.
A do-while loop executes a block of code first and then checks the condition.
do {
// statements
} while (condition);The semicolon after the condition is required.
do {
// code to execute
} while (condition);The do block contains the statements to execute, and the while condition determines whether the loop should repeat.
int i = 1;
do {
std::cout << i << std::endl;
i++;
} while (i <= 5);Output:
1
2
3
4
5A do-while loop works in this order:
do {
// execute first
} while (condition);int number = 10;
do {
std::cout << "Hello";
} while (number < 5);The condition is false because 10 is not less than 5, but Hello is still printed once.
| while Loop | do-while Loop |
|---|---|
| Checks condition before executing the body. | Checks condition after executing the body. |
| May execute zero times. | Executes at least once. |
| No semicolon after the condition. | Semicolon is required after the while condition. |
int i = 1;
do {
std::cout << i << std::endl;
i++;
} while (i <= 5);The loop prints the numbers from 1 to 5.
int i = 5;
do {
std::cout << i << std::endl;
i--;
} while (i >= 1);The loop counts backward from 5 to 1.
int i = 2;
do {
std::cout << i << std::endl;
i += 2;
} while (i <= 20);The loop prints even numbers from 2 to 20.
int i = 1;
do {
std::cout << i << std::endl;
i += 2;
} while (i <= 19);The loop prints odd numbers from 1 to 19.
#include <iostream>
int main() {
int number;
do {
std::cout << "Enter a positive number: ";
std::cin >> number;
} while (number <= 0);
std::cout << "Valid number entered";
return 0;
}The user is asked for input at least once.
The do-while loop is useful when input must be entered at least once and needs to satisfy a condition.
int marks;
do {
std::cout << "Enter marks between 0 and 100: ";
std::cin >> marks;
} while (marks < 0 || marks > 100);
std::cout << "Valid marks";int i = 1;
do {
if (i % 2 == 0) {
std::cout << i
<< " is even"
<< std::endl;
}
i++;
} while (i <= 10);The if statement checks each number generated by the loop.
int i = 1;
int sum = 0;
do {
sum += i;
i++;
} while (i <= 10);
std::cout << "Sum = " << sum;The program calculates the sum of numbers from 1 to 10.
int number = 5;
int i = 1;
do {
std::cout << number
<< " x "
<< i
<< " = "
<< number * i
<< std::endl;
i++;
} while (i <= 10);This program prints the multiplication table of 5.
int number = 5;
int factorial = 1;
int i = 1;
do {
factorial *= i;
i++;
} while (i <= number);
std::cout << "Factorial = "
<< factorial;The factorial of 5 is 120.
int choice;
do {
std::cout << "1. Add" << std::endl;
std::cout << "2. View" << std::endl;
std::cout << "3. Exit" << std::endl;
std::cout << "Enter choice: ";
std::cin >> choice;
} while (choice != 3);The menu appears at least once and continues until the user chooses 3.
#include <iostream>
int main() {
int choice;
do {
std::cout << std::endl;
std::cout << "1. Add Student" << std::endl;
std::cout << "2. View Student" << std::endl;
std::cout << "3. Exit" << std::endl;
std::cout << "Enter choice: ";
std::cin >> choice;
if (choice == 1) {
std::cout << "Add Student selected";
}
else if (choice == 2) {
std::cout << "View Student selected";
}
else if (choice == 3) {
std::cout << "Exiting...";
}
else {
std::cout << "Invalid choice";
}
} while (choice != 3);
return 0;
}The break statement can immediately terminate a do-while loop.
int i = 1;
do {
if (i == 5) {
break;
}
std::cout << i << std::endl;
i++;
} while (i <= 10);
The loop stops when i becomes 5.
The continue statement skips the remaining part of the current iteration. In a do-while loop, execution then proceeds to the condition check.
int i = 0;
do {
i++;
if (i == 3) {
continue;
}
std::cout << i << std::endl;
} while (i < 5);The number 3 is skipped.
#include <iostream>
#include <string>
int main() {
std::string password;
do {
std::cout << "Enter password: ";
std::cin >> password;
if (password != "1234") {
std::cout << "Wrong password"
<< std::endl;
}
} while (password != "1234");
std::cout << "Correct password";
return 0;
}char answer;
do {
std::cout << "Continue? (y/n): ";
std::cin >> answer;
} while (answer != 'n');
std::cout << "Program ended";The question is displayed at least once and repeats until the user enters n.
int number;
do {
std::cout << "Enter a number between 1 and 100: ";
std::cin >> number;
} while (number < 1 || number > 100);
std::cout << "Valid number";The loop continues while the number is outside the valid range.
while loop:
int number = 10;
while (number < 5) {
std::cout << "Hello";
}Here, the condition is false initially, so nothing is printed.
do-while loop:
int number = 10;
do {
std::cout << "Hello";
} while (number < 5);Here, Hello is printed once because the condition is checked after the loop body.
A do-while loop can be placed inside another do-while loop.
int i = 1;
do {
int j = 1;
do {
std::cout << i
<< ","
<< j
<< std::endl;
j++;
} while (j <= 3);
i++;
} while (i <= 3);while (condition).Correct syntax:
do {
// statements
} while (condition);#include <iostream>
int main() {
int marks;
do {
std::cout << "Enter marks between 0 and 100: ";
std::cin >> marks;
if (marks < 0 || marks > 100) {
std::cout << "Invalid marks"
<< std::endl;
}
} while (marks < 0 || marks > 100);
std::cout << "Marks accepted: "
<< marks;
return 0;
}#include <iostream>
int main() {
int choice;
do {
std::cout << std::endl;
std::cout << "1. Check Balance" << std::endl;
std::cout << "2. Deposit" << std::endl;
std::cout << "3. Withdraw" << std::endl;
std::cout << "4. Exit" << std::endl;
std::cout << "Enter choice: ";
std::cin >> choice;
switch (choice) {
case 1:
std::cout << "Balance selected";
break;
case 2:
std::cout << "Deposit selected";
break;
case 3:
std::cout << "Withdraw selected";
break;
case 4:
std::cout << "Exiting...";
break;
default:
std::cout << "Invalid choice";
}
} while (choice != 4);
return 0;
}do {
// statements
} while (condition);| Part | Purpose |
|---|---|
do |
Starts the loop body. |
| Loop Body | Executes before the condition is checked. |
while |
Checks whether another iteration should execute. |
| Condition | Controls whether the loop repeats. |
break |
Terminates the loop immediately. |
continue |
Skips the remaining part of the current iteration and proceeds to the condition check. |
do {
// statements
} while (condition);Question: What is the main difference between a while loop and a do-while loop?