Loops in c++

Loops in C++ – Complete Guide for Beginners

1. What is a Loop?

A loop is used to execute a block of code again and again until a condition becomes false.

Real-life example:

• Brushing teeth every day until the day ends

• Attending classes every day until semester ends

In programming, loops save time and reduce code repetition.

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2. Why Loops Are Important in C++?

• Avoid writing same code multiple times

• Make programs shorter and cleaner

• Required for arrays, patterns, searching, sorting

• Used in almost every real program

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3. Types of Loops in C++

C++ provides 3 main types of loops:

1. for loop

2. while loop

3. do-while loop

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4. for Loop in C++

Syntax:

for(initialization; condition; update) {
    // code
}

How it works:

1. Initialization runs once

2. Condition is checked

3. Code executes if condition is true

4. Update runs

5. Steps 2–4 repeat

Example:

for(int i = 1; i <= 5; i++) {
    cout << i << endl;
}

Output:

1
2
3
4
5

When to use for loop?

• When number of iterations is known

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5. while Loop in C++

Syntax:

while(condition) {
    // code
}

Example:

int i = 1;
while(i <= 5) {
    cout << i << endl;
    i++;
}

When to use while loop?

• When number of iterations is unknown

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6. do-while Loop in C++

Syntax:

do {
    // code
} while(condition);

Example:

int i = 1;
do {
    cout << i << endl;
    i++;
} while(i <= 5);

Important Point:

• Executes at least once even if condition is false

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7. Difference Between Loops

Feature	for	while	do-while
Condition check	Before	Before	After
Executes at least once	No	No	Yes
Best use	Known count	Unknown count	Menu programs

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8. Nested Loops

A loop inside another loop.

Example:

for(int i = 1; i <= 3; i++) {
    for(int j = 1; j <= 3; j++) {
        cout << "* ";
    }
    cout << endl;
}

Output:

* * *
* * *
* * *

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9. Infinite Loop

A loop that never ends.

Example:

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

How to stop?

• Use break

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10. break Statement

Stops the loop immediately.

for(int i = 1; i <= 10; i++) {
    if(i == 5) break;
    cout << i << endl;
}

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11. continue Statement

Skips current iteration.

for(int i = 1; i <= 5; i++) {
    if(i == 3) continue;
    cout << i << endl;
}

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12. Common Mistakes by Beginners

• Forgetting update statement

• Wrong condition

• Infinite loops

• Using wrong loop type

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13. Practice Questions

1. Print numbers from 1 to 100

2. Print even numbers

3. Reverse a number

4. Check prime number

5. Print star patterns

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14. Interview Questions

• Difference between while and do-while?

• What is infinite loop?

• When to use for loop?

• What is nested loop?

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15. Conclusion

Loops are the backbone of programming. Mastering loops makes you confident in C++ and prepares you for advanced topics like arrays, functions, and algorithms.

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