This article presents several C programming examples that demonstrate the use of functions, recursion, and various algorithms.

1. Power Calculation Using Recursion

This program calculates the power of a number using a recursive function with optimization for even exponents.

#include <stdio.h>
#include <stdlib.h>

int compute_power(int base, int exponent);

int main() {
    int base, exponent;
    int result;
    
    while (printf("Enter base and exponent: "), scanf("%d%d", &base, &exponent) != EOF) {
        result = compute_power(base, exponent);
        printf("Exponent = %d, Result = %d\n\n", exponent, result);
    }
    
    system("pause");
    return 0;
}

int compute_power(int base, int exponent) {
    int temp;
    
    if (exponent == 0)
        return 1;
    else if (exponent % 2)
        return base * compute_power(base, exponent - 1);
    else {
        temp = compute_power(base, exponent / 2);
        return temp * temp;
    }
}

2. Score to Grade Conversion

This program converts numerical scores to letter grades using a switch statement.

#include <stdio.h>
#include <stdlib.h>

char convert_score_to_grade(int score);

int main() {
    int score;
    char grade;
    
    while (scanf("%d", &score) != EOF) {
        grade = convert_score_to_grade(score);
        printf("Score: %d, Grade: %c\n\n", score, grade);
    }
    
    system("pause");
    return 0;
}

char convert_score_to_grade(int score) {
    char grade;
    
    switch (score / 10) {
        case 10:
        case 9:   grade = 'A'; break;
        case 8:   grade = 'B'; break;
        case 7:   grade = 'C'; break;
        case 6:   grade = 'D'; break;
        default:  grade = 'E';
    }
    
    return grade;
}

3. Sum of Digits Calculation

This program calculates the sum of digits of a given integer.

#include <stdio.h>
#include <stdlib.h>

int calculate_digit_sum(int number);

int main() {
    int number;
    int result;
    
    while (printf("Enter number: "), scanf("%d", &number) != EOF) {
        result = calculate_digit_sum(number);
        printf("Number = %d, Sum of digits = %d\n\n", number, result);
    }
    
    system("pause");
    return 0;
}

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

4. Prime Number and Twin Prime Identification

This program identifies prime numbers and counts twin primes (pairs of primes with difference 2) up to 100.

#include <stdio.h>
#include <stdlib.h>

int check_prime(int number);

int main() {
    int number;
    int count = 0;
    int prime1, prime2;
    
    for (number = 1; number <= 98; number++) {
        prime1 = check_prime(number);
        prime2 = check_prime(number + 2);
        
        if (prime1 == 1 && prime2 == 1) {
            printf("%d %d\n", number, number + 2);
            count += 1;
        }
    }
    
    printf("Number of twin primes under 100: %d\n", count);
    system("pause");
    return 0;
}

int check_prime(int number) {
    int divisor;
    
    if (number == 1)
        return 0;
    
    for (divisor = 2; divisor <= number / 2; divisor++) {
        if (number % divisor == 0)
            return 0;
    }
    
    return 1;
}

5. Tower of Hanoi Problem

This program solves the Tower of Hanoi problem using recursion and counts the number of moves.

#include <stdio.h>
#include <stdlib.h>

void solve_hanoi(unsigned int disks, char source, char auxiliary, char destination);
int move_disk(unsigned int disk, char source, char destination);
int move_count;

int main() {
    unsigned int disks;
    
    while (scanf("%u", &disks) != EOF) {
        solve_hanoi(disks, 'A', 'B', 'C');
        printf("Total moves: %d.\n", move_count);
        move_count = 0;
    }
    
    system("pause");
    return 0;
}

void solve_hanoi(unsigned int disks, char source, char auxiliary, char destination) {
    if (disks == 1) {
        move_disk(disks, source, destination);
    } else {
        solve_hanoi(disks - 1, source, destination, auxiliary);
        move_disk(disks, source, destination);
        solve_hanoi(disks - 1, auxiliary, source, destination);
    }
    move_count += 1;
}

int move_disk(unsigned int disk, char source, char destination) {
    printf("%u: %c -> %c\n", disk, source, destination);
}

6. Combination Calculation (Iterative and Recursive)

This program calculates combinations using both iterative and recursive approaches.

Iterative Version

#include <stdio.h>
#include <stdlib.h>

int calculate_combination(int n, int m);

int main() {
    int n, m;
    int result;
    
    while (scanf("%d%d", &n, &m) != EOF) {
        result = calculate_combination(n, m);
        printf("n = %d, m = %d, Combination = %d\n\n", n, m, result);
    }
    
    system("pause");
    return 0;
}

int calculate_combination(int n, int m) {
    int numerator = 1, denominator = 1, result;
    int i, j;
    
    if (n < m)
        return 0;
    else {
        for (i = n; i >= (n - m + 1); i--)
            numerator *= i;
        for (j = 1; j <= m; j++)
            denominator *= j;
        result = numerator / denominator;
        return result;
    }
}

Rceursive Version

#include <stdio.h>
#include <stdlib.h>

int calculate_combination(int n, int m);

int main() {
    int n, m;
    int result;
    
    while (scanf("%d%d", &n, &m) != EOF) {
        result = calculate_combination(n, m);
        printf("n = %d, m = %d, Combination = %d\n\n", n, m, result);
    }
    
    system("pause");
    return 0;
}

int calculate_combination(int n, int m) {
    int result;
    
    if (n < m)
        return 0;
    else if (m == 0)
        return 1;
    else if (m == 1)
        result = n;
    else
        result = calculate_combination(n - 1, m) + calculate_combination(n - 1, m - 1);
    
    return result;
}

7. Greatest Common Divisor of Three Numbers

This program calculates the greatest common divisor (GCD) of three numbers.

#include <stdio.h>
#include <stdlib.h>

int find_gcd(int a, int b, int c);

int main() {
    int a, b, c;
    int result;
    
    while (scanf("%d%d%d", &a, &b, &c) != EOF) {
        result = find_gcd(a, b, c);
        printf("GCD: %d\n\n", result);
    }
    
    system("pause");
    return 0;
}

int find_gcd(int a, int b, int c) {
    int minimum = a;
    
    if (b < minimum) {
        minimum = b;
    }
    
    if (c < minimum) {
        minimum = c;
    }
    
    for (int i = minimum; i >= 1; i--) {
        if (a % i == 0 && b % i == 0 && c % i == 0) {
            return i;
        }
    }
    
    return 1;
}

These examples cover various programming concepts including function implementation, recursion, mathematical calculasions, and algorithm design in C programming.