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C is a statically typed, procedural systems programming language created by Dennis Ritchie at Bell Labs in the early 1970s. Designed for efficiency and close control over memory and hardware, it provides pointers, manual memory management, and a small core language paired with a standard library. C heavily influenced the syntax of countless later languages and remains a foundation of computing.
Today C is the language of operating system kernels, embedded systems, device drivers, and performance-critical libraries. Its portability and minimal runtime make it ideal where predictability and speed matter. CompileBytes builds main.c with GCC 15.3 in GNU C23 mode inside an isolated hosted sandbox, so you can use modern C features, pointers, structs, and the standard library without installing a toolchain.
main.c is the entry point. Add helper files from the explorer and import them into your project.
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main.c includes a header containing a small inline helper.
#include <stdio.h>
#include "helper.h"
int main(void) {
printf("%d\n", answer());
return 0;
}
#ifndef HELPER_H
#define HELPER_H
static inline int answer(void) { return 42; }
#endif
#include <stdio.h>
int main(void) {
printf("Hello, World!\n");
return 0;
}#include <stdio.h>
int main(void) {
char name[100];
scanf("%99s", name);
printf("Hello, %s!\n", name);
return 0;
}#include <stdio.h>
int main(void) {
int nums[] = {10, 20, 30};
for (int i = 0; i < 3; i++) {
printf("%d\n", nums[i]);
}
return 0;
}#include <stdio.h>
long factorial(int n) {
return n <= 1 ? 1 : n * factorial(n - 1);
}
int main(void) {
printf("%ld\n", factorial(5));
return 0;
}#include <stdio.h>
#include <string.h>
int main(void) {
char s[] = "Hello, World";
printf("length: %zu\n", strlen(s));
char copy[64];
strcpy(copy, s);
printf("%s\n", copy);
return 0;
}#include <stdio.h>
struct Point {
int x, y;
};
int main(void) {
struct Point p = {3, 4};
printf("(%d, %d)\n", p.x, p.y);
return 0;
}#include <stdio.h>
#include <stdlib.h>
int cmp(const void *a, const void *b) {
const int lhs = *(const int *)a;
const int rhs = *(const int *)b;
return (lhs > rhs) - (lhs < rhs);
}
int main(void) {
int nums[] = {3, 1, 2};
qsort(nums, 3, sizeof(int), cmp);
for (int i = 0; i < 3; i++) printf("%d ", nums[i]);
printf("\n");
return 0;
}#include <stdio.h>
#include <stdlib.h>
int main(void) {
int n = 3;
int *arr = malloc(n * sizeof *arr);
if (arr == NULL) return 1;
for (int i = 0; i < n; i++) arr[i] = i * i;
for (int i = 0; i < n; i++) printf("%d\n", arr[i]);
free(arr);
return 0;
}#include <stdio.h>
void swap(int *a, int *b) {
int t = *a;
*a = *b;
*b = t;
}
int main(void) {
int x = 1, y = 2;
swap(&x, &y);
printf("%d %d\n", x, y);
return 0;
}#include <stdio.h>
int main(void) {
int n, sum = 0;
while (scanf("%d", &n) == 1) {
sum += n;
}
printf("Sum: %d\n", sum);
return 0;
}The editor uses Monaco, the engine behind VS Code, with language-aware editing tools and familiar keyboard controls.
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C is one of 23 linked-project compilers. Run always starts main.c; selecting a helper tab changes what you edit, not the entry file.
main.c includes a header containing a small inline helper.
Linked-project languages (23): Node.js, TypeScript, Deno, Python, C, Go, Dart, Swift, Rust, Ruby, PHP, Java, Kotlin, C++, C#, Nim, Crystal, Haxe, Zig, Scala, D, Bun, Objective-C.
Single-file scratchpads (46): Matplotlib, NumPy, pandas, Haskell, Clojure, Perl, Lua, Tcl, jq, Raku, Elixir, Bash, Zsh, Nushell, R, Assembly (NASM), Julia, Octave, Groovy, PowerShell, Visual Basic .NET, Odin, Pascal, Lisp, Erlang, CoffeeScript, COBOL, BASIC, V, Racket, OCaml, Prolog, AWK, Emacs Lisp, Emojicode, Forth, F#, Fortran, Assembly (NASM64), Solidity, Mojo, Ada, WASM (WAT), Gleam, Shell Script (sh), Scheme. Their extra project files are not submitted to the runtime.
Download project exports every C tab and a README in one ZIP archive.