C Programming Concepts Explained: Functions, Recursion, Loops and More

Learn C programming concepts like functions, recursion, loops, algorithms through practical examples. Master palindromes, Fibonacci, prime numbers & more!

1. Arithmetic Operations Using Functions

#include <stdio.h>

// Function to add two numbers
float add(float a, float b) {
    return a + b;
}

// Function to subtract two numbers
float subtract(float a, float b) {
    return a - b;
}

int main() {
    float num1, num2;
    
    printf("Enter two numbers: ");
    scanf("%f %f", &num1, &num2);
    
    printf("Addition: %.2f + %.2f = %.2f\n", num1, num2, add(num1, num2));
    printf("Subtraction: %.2f - %.2f = %.2f\n", num1, num2, subtract(num1, num2));
    
    return 0;
}

Output: This program takes two numbers and performs addition and subtraction using functions.

1. Arithmetic Operations

Enter two numbers: 12 5
Addition: 12.00 + 5.00 = 17.00
Subtraction: 12.00 - 5.00 = 7.00

2. Factorial Using Function

#include <stdio.h>

int factorial(int n) {
    if (n == 0 || n == 1)
        return 1;
    else
        return n * factorial(n - 1);
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("Factorial of %d is %d", num, factorial(num));
    return 0;
}

Output: Calculates factorial of a number using recursion.

2. Factorial

Enter a number: 5
Factorial of 5 is 120

3. Reverse a Number Using Function

#include <stdio.h>

int reverseNumber(int num) {
    int reversed = 0;
    while (num != 0) {
        reversed = reversed * 10 + num % 10;
        num /= 10;
    }
    return reversed;
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("Reversed number: %d", reverseNumber(num));
    return 0;
}

Output: Reverses the digits of a given number.

3. Reverse Number

Enter a number: 1234
Reversed number: 4321

4. Sum of Digits Using Function

#include <stdio.h>

int sumOfDigits(int num) {
    int sum = 0;
    while (num != 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    printf("Sum of digits: %d", sumOfDigits(num));
    return 0;
}

Output: Calculates the sum of all digits in a number.

4. Sum of Digits

Enter a number: 456
Sum of digits: 15

5. Palindrome Check Using Function

#include <stdio.h>

int isPalindrome(int num) {
    int original = num, reversed = 0;
    while (num != 0) {
        reversed = reversed * 10 + num % 10;
        num /= 10;
    }
    return original == reversed;
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (isPalindrome(num))
        printf("%d is a palindrome.", num);
    else
        printf("%d is not a palindrome.", num);
    return 0;
}

Output: Checks if a number reads the same forwards and backwards.

5. Palindrome Check

Enter a number: 1221
1221 is a palindrome.

6. Armstrong Number Check

#include <stdio.h>
#include <math.h>

int isArmstrong(int num) {
    int original = num, sum = 0, digits = 0;
    while (original != 0) {
        digits++;
        original /= 10;
    }
    original = num;
    while (original != 0) {
        sum += pow(original % 10, digits);
        original /= 10;
    }
    return num == sum;
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (isArmstrong(num))
        printf("%d is an Armstrong number.", num);
    else
        printf("%d is not an Armstrong number.", num);
    return 0;
}

Output: Checks if a number is Armstrong (sum of cubes of digits equals the number).

6. Armstrong Number

Enter a number: 153
153 is an Armstrong number.

7. Prime Number Check

#include <stdio.h>

int isPrime(int num) {
    if (num <= 1) return 0;
    for (int i = 2; i <= num/2; i++) {
        if (num % i == 0)
            return 0;
    }
    return 1;
}

int main() {
    int num;
    printf("Enter a number: ");
    scanf("%d", &num);
    if (isPrime(num))
        printf("%d is a prime number.", num);
    else
        printf("%d is not a prime number.", num);
    return 0;
}

Output: Checks if a number is prime (divisible only by 1 and itself).

7. Prime Number

Enter a number: 17
17 is a prime number.

8. Fibonacci Series Using Function

#include <stdio.h>

void fibonacci(int n) {
    int a = 0, b = 1, c;
    printf("Fibonacci Series: %d, %d", a, b);
    for (int i = 2; i < n; i++) {
        c = a + b;
        printf(", %d", c);
        a = b;
        b = c;
    }
}

int main() {
    int terms;
    printf("Enter number of terms: ");
    scanf("%d", &terms);
    fibonacci(terms);
    return 0;
}

Output: Prints Fibonacci series up to n terms (0, 1, 1, 2, 3, 5...).

8. Fibonacci Series

Enter number of terms: 6
Fibonacci Series: 0, 1, 1, 2, 3, 5

9. Macro Example

#include <stdio.h>

#define PI 3.14159
#define SQUARE(x) (x * x)

int main() {
    float radius = 5.0;
    printf("Area of circle with radius %.2f: %.2f\n", radius, PI * SQUARE(radius));
    printf("Square of 7: %d", SQUARE(7));
    return 0;
}

Output: Demonstrates use of macros for constants and simple functions.

9. Macro Example

Area of circle with radius 5.00: 78.54
Square of 7: 49

10. #include Directive Example

#include <stdio.h>
#include <string.h>  // For string functions

int main() {
    char name[20] = "Hello";
    printf("Original string: %s\n", name);
    strcat(name, " World!");  // Using function from string.h
    printf("After concatenation: %s", name);
    return 0;
}

Output: Shows how to use #include to access library functions.

10. #include Directive

Original string: Hello
After concatenation: Hello World!

All outputs are based on sample inputs

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