Advanced Coding & Software Engineering Program

Loops in C++ – Complete Tutorial

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Last Updated on: 6th Dec 2025 19:02:07 PM

1. Introduction to Loops in C++

In programming, many tasks require repeating the same set of instructions multiple times. Writing the same code again and again is inefficient and error-prone. To solve this problem, C++ provides loops.

 

Loops are used to:

• Reduce code duplication

• Automate repetitive tasks

• Process collections of data

• Build logic-based programs

 

2. Why Loops Are Important

Without loops:

• Programs would be lengthy and hard to maintain

• Repeated logic would require manual copying

• Processing arrays or large data would be impossible

 

Real-Life Examples

• Printing roll numbers of all students

• Counting total marks

• Displaying table of a number

• Repeating menu options

• Iterating over lists or arrays

 

What is a Loop?

A loop is a control statement that executes a block of code repeatedly while a specified condition remains true (or until a termination condition is reached). Each repetition is called an iteration. Loops have three parts: initialization, condition check, and update (progress toward termination).

 

3. Types of Loops in C++

C++ provides three primary types of loops:

1.  for  Loop

2.  while  Loop

3.  do–while  Loop

Additionally:

• Nested Loops

• Loop control statements: break, continue, goto

 

4.  for  Loop in C++

The for loop is used when the number of iterations is known in advance. It combines initialization, condition checking, and increment/decrement in a single line.

 

Syntax

for (initialization; condition; increment/decrement)
{
    // code block
}

 

Working

1. Initialization executes once

2. Condition is checked

3. If true → execute code

4. Increment/decrement occurs

5. Steps repeat until condition becomes false

 

Example: Print 1 to 5 

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 5; i++) {
        cout << i << " ";
    }
    return 0;
}

 

Output

1 2 3 4 5

 

Explanation

• int i = 1 — initialization

• i <= 5 — condition checked before each iteration

• ++i — update at end of each iteration

 

Real-World Example: Multiplication Table

int num = 5;
for (int i = 1; i <= 10; i++) {
    cout << num << " x " << i << " = " << num * i << endl;
}

 

5.  while  Loop in C++

The while loop executes a block of code as long as the condition is true. The condition is checked before execution. 

 

Syntax

while (condition)
{
    // code
}

 

Working

• Condition checked first

• If true → code executes

• Loop repeats until condition becomes false

 

Example: Print Numbers

#include <iostream>
using namespace std;

int main() {
    int i = 1;

    while (i <= 5) {
        cout << i << " ";
        i++;
    }
    return 0;
}

 

 Output

1 2 3 4 5

 

Use case

Use while when you don’t know how many times you will loop (e.g., read until EOF, wait for user input).

 

6.  do–while  Loop in C++

The do–while loop executes the code at least once, even if the condition is false.

 

Syntax

do
{
    // code
}
while (condition);

 

Working

• Code executes first

• Condition is checked later

• Guaranteed one execution

 

Example:

#include <iostream>
using namespace std;

int main() {
    int i = 1;

    do {
        cout << i << " ";
        i++;
    } while (i <= 5);

    return 0;
}

 

Use Case

• Menus

• Validation loops

 

7.  Nested  Loops in C++

A nested loop is a loop inside another loop. The inner loop completes fully for each iteration of the outer loop.

 

Syntax

for ( ; ; ) {
    for ( ; ; ) {
        // code
    }
}

 

Example: Star Pattern

#include <iostream>
using namespace std;

int main() {
    for (int i = 1; i <= 5; i++) {
        for (int j = 1; j <= i; j++) {
            cout << "* ";
        }
        cout << endl;
    }
    return 0;
}

 

Output

*
* *
* * *
* * * *
* * * * *

 

8. Infinite Loops

A loop that never terminates is called an infinite loop.

Example

while (true) {
    cout << "Hello";
}

 

9. Full Example Programs (copy-paste ready)

 

Example A — Sum of array using  for 

#include <iostream>
using namespace std;

int main() {
    int a[] = {1,2,3,4,5};
    int n = sizeof(a)/sizeof(a[0]);
    int sum = 0;
    for (int i = 0; i < n; ++i) sum += a[i];
    cout << "Sum is " << sum << '\n';
    return 0;
}

 

Example B — Menu loop ( do-while )

#include <iostream>
using namespace std;

int main() {
    int choice;
    do {
        cout << "1. Hello\n2. Exit\nEnter: ";
        cin >> choice;
        if (choice == 1) cout << "Hello!\n";
    } while (choice != 2);
    cout << "Goodbye\n";
    return 0;
}

 

Example C — Read ints until zero ( while )

#include <iostream>
using namespace std;

int main() {
    int x;
    cout << "Enter numbers, 0 to stop:\n";
    while (cin >> x && x != 0) {
        cout << "You entered: " << x << '\n';
    }
    return 0;
}

10. Practical Programs Using Loops

• Print numbers 1 to 100 using a for loop.

• Print multiplication table of a number.

• Sum of numbers

• Factorial

• Fibonacci series

• Prime number

• Reverse a number

• Palindrome check

• Print multiplication table of a number.

 

 11. Quick Reference Table

Loop Type	Condition Check	Runs at least once?	Typical Use
for	before each iter	No	Known iteration count
while	before each iter	No	Unknown count, pre-check
do…while	after each iter	Yes	Menu, guarantee one run

 

12. Conclusion

• Loops are fundamental for repetition and automation.

• Use the right loop for the scenario: for when count is known, while when waiting on condition, do…while when you need one guaranteed run.

• Prefer range-based for for readability with containers.

• Use break and continue judiciously.

• Watch out for infinite loops and performance inside loops.

 

Keep practicing — you're doing amazing!

Happy Coding!    

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