The while loop is used to repeatedly execute a block of code as long as a specified condition is true. It is useful when the number of repetitions is not known in advance.
A while loop repeats a block of statements while its condition remains true.
while (condition) {
// statements
}When the condition becomes false, the loop stops.
while (condition) {
// code to repeat
}The condition is written inside parentheses, and the repeated statements are written inside curly braces.
int i = 1;
while (i <= 5) {
std::cout << i << std::endl;
i++;
}Output:
1
2
3
4
5In a while loop, the loop variable is usually initialized before the while statement.
int i = 1;
while (i <= 5) {
std::cout << i;
i++;
}
Here, i starts with the value 1.
The condition determines whether the loop body should execute.
int i = 1;
while (i <= 5) {
std::cout << i;
i++;
}
The loop continues while i <= 5 is true.
The loop variable should normally be updated inside the loop. Otherwise, the condition may never become false.
int i = 1;
while (i <= 5) {
std::cout << i;
i++;
}Consider this example:
int i = 1;
while (i <= 3) {
std::cout << i;
i++;
}i starts with 1.i <= 3 is checked.i++ increases the value.int i = 1;
while (i <= 10) {
std::cout << i << std::endl;
i++;
}This prints numbers from 1 through 10.
int i = 10;
while (i >= 1) {
std::cout << i << std::endl;
i--;
}The loop counts backward from 10 to 1.
int i = 2;
while (i <= 20) {
std::cout << i << std::endl;
i += 2;
}The value increases by 2, so only even numbers are printed.
int i = 1;
while (i <= 19) {
std::cout << i << std::endl;
i += 2;
}#include <iostream>
int main() {
int n;
std::cout << "Enter a number: ";
std::cin >> n;
int i = 1;
while (i <= n) {
std::cout << i << std::endl;
i++;
}
return 0;
}The number of iterations depends on the value entered by the user.
An if statement can be placed inside a while loop.
int i = 1;
while (i <= 10) {
if (i % 2 == 0) {
std::cout << i << std::endl;
}
i++;
}This program prints the even numbers from 1 to 10.
int i = 1;
int sum = 0;
while (i <= 10) {
sum += i;
i++;
}
std::cout << "Sum = " << sum;The program adds all numbers from 1 to 10.
int number = 5;
int i = 1;
while (i <= 10) {
std::cout << number
<< " x "
<< i
<< " = "
<< number * i
<< std::endl;
i++;
}This program prints the multiplication table of 5.
int number = 5;
int factorial = 1;
int i = 1;
while (i <= number) {
factorial *= i;
i++;
}
std::cout << "Factorial = "
<< factorial;The factorial of 5 is 120.
A while loop is useful when the number of iterations is not known in advance.
int number;
std::cout << "Enter a positive number: ";
std::cin >> number;
while (number <= 0) {
std::cout << "Enter again: ";
std::cin >> number;
}
std::cout << "Valid number entered";The loop continues until the user enters a positive number.
#include <iostream>
#include <string>
int main() {
std::string password;
std::cout << "Enter password: ";
std::cin >> password;
while (password != "1234") {
std::cout << "Wrong password. Try again: ";
std::cin >> password;
}
std::cout << "Correct password";
return 0;
}The loop continues until the correct password is entered.
The break statement immediately terminates a while loop.
int i = 1;
while (i <= 10) {
if (i == 5) {
break;
}
std::cout << i << std::endl;
i++;
}
The loop stops when i becomes 5.
The continue statement skips the remaining statements of the current iteration and moves to the next iteration.
int i = 0;
while (i < 5) {
i++;
if (i == 3) {
continue;
}
std::cout << i << std::endl;
}The number 3 is skipped.
An infinite loop is a loop whose condition never becomes false.
int i = 1;
while (i <= 5) {
std::cout << i;
// i is never updated
}
This loop keeps running because i remains 1.
Always make sure the loop can eventually reach a false condition,
unless an intentional infinite loop is required.
int numbers[] = {10, 20, 30, 40, 50};
int i = 0;
while (i < 5) {
std::cout << numbers[i]
<< std::endl;
i++;
}The loop accesses each array element using its index.
#include <iostream>
#include <string>
int main() {
std::string name = "SOOPRO";
int i = 0;
while (i < name.length()) {
std::cout << name[i]
<< std::endl;
i++;
}
return 0;
}The loop prints each character of the string.
#include <iostream>
int main() {
int choice = 0;
while (choice != 4) {
std::cout << "1. Add" << std::endl;
std::cout << "2. View" << std::endl;
std::cout << "3. Delete" << std::endl;
std::cout << "4. Exit" << std::endl;
std::cout << "Enter choice: ";
std::cin >> choice;
if (choice == 1) {
std::cout << "Add selected" << std::endl;
}
else if (choice == 2) {
std::cout << "View selected" << std::endl;
}
else if (choice == 3) {
std::cout << "Delete selected" << std::endl;
}
else if (choice != 4) {
std::cout << "Invalid choice" << std::endl;
}
}
return 0;
}A while loop can be placed inside another while loop.
int i = 1;
while (i <= 3) {
int j = 1;
while (j <= 3) {
std::cout << i
<< ","
<< j
<< std::endl;
j++;
}
i++;
}Both loops can repeat code, but their common uses are slightly different.
| for Loop | while Loop |
|---|---|
| Often used when the number of iterations is known. | Often used when the stopping condition is more important than a fixed count. |
| Initialization, condition, and update appear together. | Initialization and update are usually written separately. |
| Compact for counter-based loops. | Useful for input validation and condition-controlled repetition. |
#include <iostream>
int main() {
int n;
std::cout << "Enter a number: ";
std::cin >> n;
int i = 1;
while (i <= n) {
if (i % 2 == 0) {
std::cout << i
<< " is even"
<< std::endl;
}
else {
std::cout << i
<< " is odd"
<< std::endl;
}
i++;
}
return 0;
}#include <iostream>
int main() {
int choice = 0;
while (choice != 3) {
std::cout << "1. Check Balance"
<< std::endl;
std::cout << "2. Deposit"
<< std::endl;
std::cout << "3. Exit"
<< std::endl;
std::cout << "Enter choice: ";
std::cin >> choice;
switch (choice) {
case 1:
std::cout << "Balance selected"
<< std::endl;
break;
case 2:
std::cout << "Deposit selected"
<< std::endl;
break;
case 3:
std::cout << "Exiting..."
<< std::endl;
break;
default:
std::cout << "Invalid choice"
<< std::endl;
}
}
return 0;
}Correct example:
int i = 1;
while (i <= 5) {
std::cout << i;
i++;
}| Part | Purpose |
|---|---|
| Initialization | Sets the starting value before the loop. |
| Condition | Determines whether the loop continues. |
| Loop Body | Contains the statements that are repeated. |
| Update | Changes the loop variable so the loop can eventually stop. |
| break | Immediately terminates the loop. |
| continue | Skips the current iteration. |
int i = 1;
while (i <= 10) {
std::cout << i;
i++;
}Question: When is the condition of a while loop checked?