C Cheat Sheet

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

// Single line comment
/* Multi-line
   comment */

int age = 25;
long count = 1000000;
short num = 32000;

float price = 19.99f;
double pi = 3.14159265359;

char letter = 'A';
char name[] = "John";

const int MAX = 100;
#define PI 3.14159

int x = 10;
float y = (float)x;
int z = (int)3.14;

int a = 5 + 3;  // 8
int b = 5 - 3;  // 2
int c = 5 * 3;  // 15
int d = 5 / 3;  // 1
int e = 5 % 3;  // 2

5 == 5  // 1 (true)
5 != 3  // 1 (true)
5 > 3   // 1 (true)
5 < 3   // 0 (false)

(5 > 3) && (2 < 4)  // 1 (true)
(5 > 3) || (2 > 4)  // 1 (true)
!(5 > 3)             // 0 (false)

int x = 5;
x++;  // 6 (post-increment)
++x;  // 7 (pre-increment)
x--;  // 6 (post-decrement)
--x;  // 5 (pre-decrement)

if (x > 0) {
    printf("positive");
} else if (x < 0) {
    printf("negative");
} else {
    printf("zero");
}

switch (day) {
    case 1:
        printf("Monday");
        break;
    case 2:
        printf("Tuesday");
        break;
    default:
        printf("Other");
}

for (int i = 0; i < 10; i++) {
    printf("%d\n", i);
}

int i = 0;
while (i < 10) {
    printf("%d\n", i);
    i++;
}

int i = 0;
do {
    printf("%d\n", i);
    i++;
} while (i < 10);

int numbers[5];
int nums[] = {1, 2, 3, 4, 5};

int first = nums[0];
nums[1] = 10;

int matrix[3][3] = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

char name[] = "John";
char greeting[20] = "Hello";

int add(int a, int b) {
    return a + b;
}

int result = add(5, 3);  // 8

void greet() {
    printf("Hello!\n");
}

// Declare before use
int multiply(int a, int b);

int main() {
    int result = multiply(3, 4);
    return 0;
}

int multiply(int a, int b) {
    return a * b;
}

int x = 10;
int *ptr = &x;  // ptr stores address of x

int value = *ptr;  // Get value at address
*ptr = 20;         // Modify value

int *ptr = NULL;

int arr[] = {1, 2, 3};
int *p = arr;
p++;  // Move to next element

struct Person {
    char name[50];
    int age;
    float height;
};

struct Person person1;
strcpy(person1.name, "John");
person1.age = 30;

struct Person person2 = {
    "Jane",
    25,
    5.6
};

typedef struct {
    char name[50];
    int age;
} Person;

Person p;  // No 'struct' needed