C Examples: Practical Programming

Learning syntax is only half the battle. To become a proficient C programmer, you must see how different libraries work together to solve logic-based problems.

1. The "Number Guessing" Game

This example uses stdlib.h for random numbers, time.h for seeding, and stdio.h for user interaction.

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

int main() {
    int secret, guess;
    srand(time(0)); // Seed random number generator
    secret = rand() % 100 + 1; // Number between 1-100

    do {
        printf("Guess (1-100): ");
        scanf("%d", &guess);
        if (guess > secret) printf("Lower!\n");
        else if (guess < secret) printf("Higher!\n");
    } while (guess != secret);

    printf("Bingo! The number was %d", secret);
    return 0;
}

2. Password Strength Checker

This program uses ctype.h and string.h to validate if a string contains digits and letters.

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main() {
    char pass[20];
    int hasDigit = 0, hasAlpha = 0;

    printf("Create Password: ");
    scanf("%s", pass);

    for(int i = 0; i < strlen(pass); i++) {
        if (isdigit(pass[i])) hasDigit = 1;
        if (isalpha(pass[i])) hasAlpha = 1;
    }

    if (hasDigit && hasAlpha && strlen(pass) >= 8)
        printf("Strong Password!");
    else
        printf("Weak Password: Need 8+ chars, letters, and numbers.");
    return 0;
}

3. Geometric Calculator

Using math.h to calculate the Hypotenuse of a triangle using Pythagoras theorem ($a^2 + b^2 = c^2$).

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

int main() {
    double a, b, c;
    printf("Enter Side A and B: ");
    scanf("%lf %lf", &a, &b);

    c = sqrt(pow(a, 2) + pow(b, 2));
    printf("Hypotenuse: %.2f", c);
    return 0;
}

4. Array Reversal

A classic logic problem demonstrating how to swap elements in an array using a loop.

int arr[] = {1, 2, 3, 4, 5};
int n = 5;
for (int i = 0; i < n / 2; i++) {
    int temp = arr[i];
    arr[i] = arr[n - 1 - i];
    arr[n - 1 - i] = temp;
}

Pro Tip: When testing these examples, always use a compiler like GCC and try to modify the logic. For instance, in the password checker, try adding a check for special characters using ispunct()!