Here are 15 classic C programs that cover fundamental programming concepts. Each program is self-contained and ready to compile with GCC.
#include <stdio.h>
int main() {
printf("Hello, World!\n");
return 0;
}#include <stdio.h>
int main() {
int a, b, sum;
printf("Enter two integers: ");
scanf("%d %d", &a, &b);
sum = a + b;
printf("Sum of %d and %d = %d\n", a, b, sum);
return 0;
}#include <stdio.h>
int main() {
int n;
long long fact = 1;
printf("Enter a positive integer: ");
scanf("%d", &n);
if (n < 0) {
printf("Factorial not defined for negative numbers.\n");
} else {
for (int i = 1; i <= n; i++) fact *= i;
printf("%d! = %lld\n", n, fact);
}
return 0;
}
/* Output: 5! = 120 */#include <stdio.h>
long long factorial(int n) {
if (n == 0 || n == 1) return 1;
return n * factorial(n - 1);
}
int main() {
int n;
printf("Enter a positive integer: ");
scanf("%d", &n);
printf("%d! = %lld\n", n, factorial(n));
return 0;
}#include <stdio.h>
int main() {
int n;
printf("Enter number of terms: ");
scanf("%d", &n);
long long a = 0, b = 1, c;
printf("Fibonacci series: ");
for (int i = 0; i < n; i++) {
printf("%lld ", a);
c = a + b;
a = b;
b = c;
}
printf("\n");
return 0;
}
/* Output (n=8): 0 1 1 2 3 5 8 13 */#include <stdio.h>
#include <math.h>
int isPrime(int n) {
if (n < 2) return 0;
if (n == 2) return 1;
if (n % 2 == 0) return 0;
for (int i = 3; i <= (int)sqrt(n); i += 2) {
if (n % i == 0) return 0;
}
return 1;
}
int main() {
int n;
printf("Enter a number: ");
scanf("%d", &n);
printf("%d is %s\n", n, isPrime(n) ? "prime" : "not prime");
// Print all primes up to 50
printf("Primes up to 50: ");
for (int i = 2; i <= 50; i++) {
if (isPrime(i)) printf("%d ", i);
}
printf("\n");
return 0;
}
/* Compile: gcc prime.c -o prime -lm */#include <stdio.h>
int main() {
int n, original, reversed = 0, digit;
printf("Enter a number: ");
scanf("%d", &n);
original = n;
while (n != 0) {
digit = n % 10;
reversed = reversed * 10 + digit;
n /= 10;
}
if (original == reversed)
printf("%d is a palindrome\n", original);
else
printf("%d is not a palindrome\n", original);
return 0;
}
/* 121 -> palindrome, 123 -> not palindrome */#include <stdio.h>
#include <string.h>
void reverseString(char str[]) {
int len = strlen(str);
for (int i = 0; i < len / 2; i++) {
char temp = str[i];
str[i] = str[len - 1 - i];
str[len - 1 - i] = temp;
}
}
int main() {
char str[100];
printf("Enter a string: ");
fgets(str, sizeof(str), stdin);
str[strcspn(str, "\n")] = '\0'; // remove newline
printf("Original: %s\n", str);
reverseString(str);
printf("Reversed: %s\n", str);
return 0;
}
/* "Hello" -> "olleH" */#include <stdio.h>
#include <string.h>
#include <ctype.h>
int isPalindrome(char str[]) {
int len = strlen(str);
for (int i = 0; i < len / 2; i++) {
if (tolower(str[i]) != tolower(str[len - 1 - i])) return 0;
}
return 1;
}
int main() {
char words[][20] = {"racecar", "hello", "madam", "level", "world"};
for (int i = 0; i < 5; i++) {
printf("%-10s -> %s\n", words[i],
isPalindrome(words[i]) ? "palindrome" : "not palindrome");
}
return 0;
}
/* racecar -> palindrome, hello -> not palindrome */#include <stdio.h>
void bubbleSort(int arr[], int n) {
for (int i = 0; i < n - 1; i++) {
int swapped = 0;
for (int j = 0; j < n - 1 - i; j++) {
if (arr[j] > arr[j + 1]) {
int temp = arr[j];
arr[j] = arr[j + 1];
arr[j + 1] = temp;
swapped = 1;
}
}
if (!swapped) break; // already sorted
}
}
int main() {
int arr[] = {64, 34, 25, 12, 22, 11, 90};
int n = sizeof(arr) / sizeof(arr[0]);
printf("Before: ");
for (int i = 0; i < n; i++) printf("%d ", arr[i]);
bubbleSort(arr, n);
printf("\nAfter: ");
for (int i = 0; i < n; i++) printf("%d ", arr[i]);
printf("\n");
return 0;
}
/* After: 11 12 22 25 34 64 90 */#include <stdio.h>
int binarySearch(int arr[], int n, int target) {
int low = 0, high = n - 1;
while (low <= high) {
int mid = low + (high - low) / 2;
if (arr[mid] == target) return mid;
else if (arr[mid] < target) low = mid + 1;
else high = mid - 1;
}
return -1; // not found
}
int main() {
int arr[] = {2, 5, 8, 12, 16, 23, 38, 56, 72, 91};
int n = sizeof(arr) / sizeof(arr[0]);
int target = 23;
int idx = binarySearch(arr, n, target);
if (idx != -1)
printf("%d found at index %d\n", target, idx);
else
printf("%d not found\n", target);
return 0;
}
/* 23 found at index 5 */#include <stdio.h>
int main() {
int a = 5, b = 10;
printf("Original: a=%d, b=%d\n", a, b);
// Method 1: Using temp variable
int temp = a; a = b; b = temp;
printf("After temp swap: a=%d, b=%d\n", a, b);
// Method 2: Using XOR (no temp variable)
a = 5; b = 10;
a = a ^ b;
b = a ^ b;
a = a ^ b;
printf("After XOR swap: a=%d, b=%d\n", a, b);
// Method 3: Using pointers
void swapPtr(int *x, int *y);
a = 5; b = 10;
swapPtr(&a, &b);
printf("After ptr swap: a=%d, b=%d\n", a, b);
return 0;
}
void swapPtr(int *x, int *y) {
int t = *x; *x = *y; *y = t;
}#include <stdio.h>
int main() {
int arr[] = {34, 78, 12, 56, 90, 23, 45};
int n = sizeof(arr) / sizeof(arr[0]);
int largest = arr[0], smallest = arr[0];
int largestIdx = 0, smallestIdx = 0;
for (int i = 1; i < n; i++) {
if (arr[i] > largest) { largest = arr[i]; largestIdx = i; }
if (arr[i] < smallest) { smallest = arr[i]; smallestIdx = i; }
}
printf("Array: ");
for (int i = 0; i < n; i++) printf("%d ", arr[i]);
printf("\nLargest: %d (index %d)\n", largest, largestIdx);
printf("Smallest: %d (index %d)\n", smallest, smallestIdx);
return 0;
}
/* Largest: 90 (index 4), Smallest: 12 (index 2) */#include <stdio.h>
#define N 3
int main() {
int a[N][N] = {{1,2,3},{4,5,6},{7,8,9}};
int b[N][N] = {{9,8,7},{6,5,4},{3,2,1}};
int c[N][N] = {0};
// Matrix multiplication: c[i][j] = sum of a[i][k] * b[k][j]
for (int i = 0; i < N; i++)
for (int j = 0; j < N; j++)
for (int k = 0; k < N; k++)
c[i][j] += a[i][k] * b[k][j];
printf("Result of A x B:\n");
for (int i = 0; i < N; i++) {
for (int j = 0; j < N; j++) printf("%5d", c[i][j]);
printf("\n");
}
return 0;
}
/*
30 24 18
84 69 54
138 114 90
*/#include <stdio.h>
#include <ctype.h>
#include <string.h>
int isVowel(char c) {
c = tolower(c);
return c=='a' || c=='e' || c=='i' || c=='o' || c=='u';
}
int main() {
char str[200];
printf("Enter a string: ");
fgets(str, sizeof(str), stdin);
int vowels = 0, consonants = 0, spaces = 0, digits = 0;
for (int i = 0; str[i] != '\0'; i++) {
if (isalpha(str[i])) {
if (isVowel(str[i])) vowels++;
else consonants++;
} else if (isspace(str[i])) spaces++;
else if (isdigit(str[i])) digits++;
}
printf("Vowels: %d\n", vowels);
printf("Consonants: %d\n", consonants);
printf("Spaces: %d\n", spaces);
printf("Digits: %d\n", digits);
return 0;
}
/* "Hello World 123" -> Vowels:3, Consonants:7, Spaces:2, Digits:3 */Explore 500+ free tutorials across 20+ languages and frameworks.