🟢 Beginner · Lesson 13

for Loop

for Loop Syntax

The for loop is the most commonly used loop in C. It's used when you know exactly how many times you want to repeat a block of code.

Syntax

for (initialization; condition; update) {
    // Body: code to repeat
}
// initialization: runs once at start   → int i = 0
// condition:      checked before each iteration → i < 10
// update:         runs after each iteration    → i++

How the for Loop Works

Initialize: int i = 1 — sets up the loop variable once
Check condition: i <= 5 — if false, exit loop
Execute body: run the code inside { }
Update: i++ — increment/decrement the variable
Go back to step 2

Examples

Example 1: Print 1 to 10

C Language

#include <stdio.h>
int main() {
    for (int i = 1; i <= 10; i++) {
        printf("%d ", i);
    }
    printf("\\n");
    return 0;
}

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Example 2: Sum of First N Numbers

C Language

#include <stdio.h>
int main() {
    int n, sum = 0;
    printf("Enter N: ");
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        sum += i;
    }
    printf("Sum of 1 to %d = %d\\n", n, sum);
    return 0;
}

Enter N: 10 Sum of 1 to 10 = 55

Example 3: Multiplication Table

C Language

#include <stdio.h>
int main() {
    int num;
    printf("Enter number: ");
    scanf("%d", &num);
    printf("\\n--- Table of %d ---\\n", num);
    for (int i = 1; i <= 10; i++) {
        printf("%d x %d = %d\\n", num, i, num * i);
    }
    return 0;
}

Enter number: 5 --- Table of 5 --- 5 x 1 = 5 5 x 2 = 10 5 x 3 = 15 ... (up to 10)

Example 4: Factorial

C Language

#include <stdio.h>
int main() {
    int n;
    long long fact = 1;
    printf("Enter n: ");
    scanf("%d", &n);
    for (int i = 1; i <= n; i++) {
        fact *= i;
    }
    printf("%d! = %lld\\n", n, fact);
    return 0;
}

Enter n: 6 6! = 720

Nested for Loop

A loop inside another loop. The inner loop completes all its iterations for each iteration of the outer loop.

C Language – 2D Pattern

#include <stdio.h>
int main() {
    int rows = 4;
    for (int i = 1; i <= rows; i++) {
        for (int j = 1; j <= i; j++) {
            printf("* ");
        }
        printf("\\n");
    }
    return 0;
}

* * * * * * * * * *

More Pattern Programs

Number Triangle

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

1 1 2 1 2 3 1 2 3 4 1 2 3 4 5

💡 for Loop Variations

for (;;) — infinite loop (no initialization, condition, update)
for (int i=10; i>=1; i--) — count down
for (int i=0; i<100; i+=5) — step by 5

Summary

for loop is used when the number of iterations is known
Syntax: for (init; condition; update) { body }
Initialization runs once; condition checked before each iteration
Nested loops: inner loop runs completely for each outer loop iteration
Common uses: counting, summing, tables, arrays, patterns

🏋️ Practice

Write programs: (1) Sum of even numbers 1-100 (2) Print all prime numbers up to N (3) Fibonacci series up to N terms (4) Right-angled star triangle (5) Inverted star pattern.

for Loop का Syntax

for loop C में सबसे commonly used loop है। इसे तब use करते हैं जब आपको पहले से पता हो कि loop कितनी बार चलना है।

Syntax

for (initialization; condition; update) {
    // Body: जो code repeat करना है
}
// initialization: शुरू में एक बार चलता है → int i = 1
// condition:      हर iteration से पहले check होती है → i <= 10
// update:         हर iteration के बाद चलता है → i++

for Loop कैसे काम करता है

Initialize: int i = 1 — एक बार loop variable set करो
Condition check: i <= 5 — false है तो loop exit
Body execute: { } के अंदर का code run करो
Update: i++ — variable increment/decrement करो
Step 2 पर वापस जाओ

Examples

Example 1: 1 से 10 Print करना

C Language

for (int i = 1; i <= 10; i++) {
    printf("%d ", i);
}

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Example 2: N तक का Sum

C Language

int n, sum = 0;
scanf("%d", &n);
for (int i = 1; i <= n; i++) sum += i;
printf("Sum = %d\\n", sum);

Example 3: Pahada (Multiplication Table)

C Language

int num = 5;
for (int i = 1; i <= 10; i++) {
    printf("%d x %d = %d\\n", num, i, num*i);
}

5 x 1 = 5 5 x 2 = 10 ... (10 तक)

Nested for Loop

एक loop के अंदर दूसरा loop। हर outer loop iteration के लिए inner loop पूरा complete होता है।

Star Pattern

for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= i; j++) printf("* ");
    printf("\\n");
}

* * * * * * * * * *

सारांश

for loop तब use करें जब iterations की संख्या पहले से पता हो
Syntax: for (init; condition; update) { body }
Initialization एक बार चलती है; condition हर iteration से पहले check होती है
Common uses: गिनती, sum, tables, arrays, patterns

🏋️ Practice

Programs लिखें: (1) 1 से 100 तक even numbers का sum (2) N तक prime numbers (3) N terms तक Fibonacci series (4) Right-angled star triangle (5) Inverted star pattern।

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