C Quick Reference

#include <stdio.h>

int main(void) {
    printf("Hello\n");
    return 0;
}

int count = 10;

double price = 9.99;

char grade = 'A';

const int MAX = 100;

#define MAX 100

#include <stdbool.h>
bool done = false;

printf("%s is %d, %.2f\n", name, age, price);

int n;
scanf("%d", &n);

sizeof(int)

if (x > 0) {
    /* ... */
} else {
    /* ... */
}

switch (c) {
    case 'a': handle(); break;
    default: other();
}

for (int i = 0; i < n; i++) { }

while (running) { }

do {
    /* runs at least once */
} while (again);

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

int len = sizeof nums / sizeof nums[0];

char name[] = "Ada";

#include <string.h>
strlen(s)

strncpy(dest, src, sizeof dest - 1);

strcmp(a, b) == 0

strncat(dest, src, sizeof dest - strlen(dest) - 1);

snprintf(buf, sizeof buf, "%d items", n);

long n = strtol(text, NULL, 10);

int x = 5;
int *p = &x;   // address of x
*p = 6;        // change x through p

void inc(int *n) { (*n)++; }
inc(&count);

#include <stdlib.h>
int *arr = malloc(n * sizeof *arr);
if (arr == NULL) { /* handle */ }

calloc(n, sizeof(int))

arr = realloc(arr, new_n * sizeof *arr);

free(arr);
arr = NULL;

struct Point {
    int x;
    int y;
};
struct Point p = {1, 2};

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

p.x

ptr->x

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

int add(int a, int b);

enum Color { RED, GREEN, BLUE };

FILE *f = fopen("out.txt", "w");
fprintf(f, "%d\n", n);
fclose(f);

char line[256];
while (fgets(line, sizeof line, f)) {
    /* ... */
}

gcc main.c -o app && ./app

gcc -Wall -Wextra -g main.c -o app

int main(int argc, char *argv[]) { }