Loops in C

Imagine you want to print "Welcome to KauraX" 100 times.

One way is to write:

cCopy
printf("Welcome to KauraX");
printf("Welcome to KauraX");
printf("Welcome to KauraX");
...

This is inefficient and time-consuming.

Instead, C provides loops, which allow us to execute the same block of code repeatedly until a specified condition becomes false.

Loops reduce code duplication, improve readability, and make programs more efficient.

🎯 Learning Objectives

After completing this lesson, you will be able to:

• Understand the concept of loops.
• Learn different types of loops.
• Write programs using while, do-while, and for.
• Understand nested loops.
• Learn infinite loops.
• Use break and continue.
• Solve practical programming problems using loops.

📖 What is a Loop?

A loop is a control structure that executes a block of code repeatedly as long as a given condition is true.

Instead of writing the same code multiple times, you can place it inside a loop.

Why Do We Need Loops?

Suppose you want to print numbers from 1 to 100.

Without loops:

cCopy
printf("1\n");
printf("2\n");
printf("3\n");
...
printf("100\n");

With loops:

cCopy
for(int i=1;i<=100;i++)
{
    printf("%d\n",i);
}

The second approach is much shorter, easier to understand, and easier to maintain.

Types of Loops in C

C provides three looping statements.

• while
• do-while
• for

The while Loop

The while loop checks the condition before executing the loop body.

If the condition is false initially, the loop will never execute.

Syntax

cCopy
while(condition)
{
    statements;
}

Flow of while Loop

textCopy
Condition
    │
True ─────► Execute Statements
    ▲            │
    └────────────┘

False
   │
 Exit Loop

Example 1

cCopy
#include <stdio.h>

int main()
{
    int i = 1;

    while(i <= 5)
    {
        printf("%d\n", i);
        i++;
    }

    return 0;
}

Output

textCopy
1
2
3
4
5

Printing KauraX Five Times

cCopy
#include <stdio.h>

int main()
{
    int i = 1;

    while(i <= 5)
    {
        printf("Welcome to KauraX\n");
        i++;
    }

    return 0;
}

The do-while Loop

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

Syntax

cCopy
do
{
    statements;
}
while(condition);

Flow of do-while Loop

textCopy
Execute Statements
       │
       ▼
 Check Condition
       │
 True ─────► Repeat
 False ────► Exit

Example

cCopy
#include <stdio.h>

int main()
{
    int i = 1;

    do
    {
        printf("%d\n", i);
        i++;
    }
    while(i <= 5);

    return 0;
}

Output

textCopy
1
2
3
4
5

Difference Between while and do-while

The for Loop

The for loop is the most commonly used loop in C.

Syntax

cCopy
for(initialization; condition; update)
{
    statements;
}

Flow of for Loop

textCopy
Initialization
      │
      ▼
 Condition
      │
 True ─────► Execute Statements
      ▲              │
      │              ▼
      └──────── Update

False
 │
 Exit Loop

Example

cCopy
#include <stdio.h>

int main()
{
    int i;

    for(i = 1; i <= 5; i++)
    {
        printf("%d\n", i);
    }

    return 0;
}

Output

textCopy
1
2
3
4
5

Printing Even Numbers

cCopy
#include <stdio.h>

int main()
{
    int i;

    for(i = 2; i <= 20; i += 2)
    {
        printf("%d ", i);
    }

    return 0;
}

Output

textCopy
2 4 6 8 10 12 14 16 18 20

Printing Odd Numbers

cCopy
#include <stdio.h>

int main()
{
    int i;

    for(i = 1; i <= 19; i += 2)
    {
        printf("%d ", i);
    }

    return 0;
}

Sum of First 10 Numbers

cCopy
#include <stdio.h>

int main()
{
    int i, sum = 0;

    for(i = 1; i <= 10; i++)
    {
        sum += i;
    }

    printf("Sum = %d", sum);

    return 0;
}

Output

textCopy
Sum = 55

Multiplication Table

cCopy
#include <stdio.h>

int main()
{
    int n, i;

    printf("Enter a number: ");
    scanf("%d", &n);

    for(i = 1; i <= 10; i++)
    {
        printf("%d x %d = %d\n", n, i, n * i);
    }

    return 0;
}

Nested Loops

A loop inside another loop is called a nested loop.

Example

cCopy
#include <stdio.h>

int main()
{
    int i, j;

    for(i = 1; i <= 3; i++)
    {
        for(j = 1; j <= 3; j++)
        {
            printf("* ");
        }

        printf("\n");
    }

    return 0;
}

Output

textCopy
* * *
* * *
* * *

Infinite Loop

A loop that never ends is called an infinite loop.

Example

cCopy
while(1)
{
    printf("KauraX");
}

Be careful while writing loop conditions.

break Statement

The break statement immediately terminates the loop.

Example

cCopy
#include <stdio.h>

int main()
{
    int i;

    for(i = 1; i <= 10; i++)
    {
        if(i == 6)
            break;

        printf("%d ", i);
    }

    return 0;
}

Output

textCopy
1 2 3 4 5

continue Statement

The continue statement skips the current iteration and moves to the next one.

Example

cCopy
#include <stdio.h>

int main()
{
    int i;

    for(i = 1; i <= 5; i++)
    {
        if(i == 3)
            continue;

        printf("%d ", i);
    }

    return 0;
}

Output

textCopy
1 2 4 5

Common Beginner Mistakes

Forgetting to Update the Loop Variable

Wrong

cCopy
while(i <= 5)
{
    printf("%d", i);
}

This creates an infinite loop.

Correct

cCopy
i++;

Incorrect Loop Condition

Wrong

cCopy
for(i = 1; i >= 10; i++)

The loop never executes.

Missing Braces

Always use braces for better readability.

Whenever writing a loop, ask yourself three questions:

1. Where does it start?
2. When does it stop?
3. How does it change after each iteration?

Best Practices

• Choose the right loop for the problem.
• Avoid infinite loops unless intentionally required.
• Use meaningful variable names.
• Keep loop conditions simple.
• Indent your code properly.

🧠 Interview Questions

1. What is a loop?
2. Differentiate between while and do-while.
3. Explain the syntax of the for loop.
4. What is a nested loop?
5. What is an infinite loop?
6. What is the difference between break and continue?
7. Which loop executes at least once?

✍ Practice Questions

1. Print numbers from 1 to 100.
2. Print even numbers between 1 and 50.
3. Print odd numbers between 1 and 50.
4. Find the sum of the first N natural numbers.
5. Print the multiplication table of any number.
6. Print a square star pattern.
7. Print numbers in reverse order.
8. Find the factorial of a number.
9. Reverse a number.
10. Count the number of digits in an integer.

📚 Lesson Summary

In this lesson, you learned:

• What loops are.
• while loop.
• do-while loop.
• for loop.
• Nested loops.
• Infinite loops.
• break statement.
• continue statement.
• Best practices and common mistakes.

Loops are one of the most powerful programming concepts. They allow programs to perform repetitive tasks efficiently and are used extensively in real-world software development.

🚀 What's Next?

In the next lesson, Functions in C, you'll learn:

• What functions are.
• Function declaration.
• Function definition.
• Function calling.
• Return values.
• Function parameters.
• Call by Value.
• Recursion.
• Practical examples.

Functions help divide large programs into smaller, reusable, and easier-to-maintain modules.

Happy Coding with KauraX 💙