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Online C Compiler and Playground

Browser-based compiler and playground for C — Progsity IDE.

About C

C remains the lingua franca of systems programming: operating systems, embedded devices, and performance-critical libraries are still written in C. This online C compiler lets you compile and run small programs instantly—perfect for learning pointers, structs, and the standard library without configuring GCC locally.

Output shows stdout, stderr, compile errors, exit code, and timing so you can distinguish logic bugs from undefined behavior. Use it for K&R-style exercises, competitive programming warm-ups, and verifying snippets before you paste them into a larger codebase.

Pair the editor with stdin when you need scanf-style input. Signed-in users can save snippets and share links—handy for assignments and code review.

How to use

  1. Write a complete C program with int main(void) or int main(int argc, char **argv). The default template prints Hello, World.
  2. If you use scanf or fgets from stdin, put test input in the stdin panel, then Run.
  3. Fix compile errors shown in the compile output tab, then re-run until you see the expected stdout.

FAQ

Is this C compiler free to use?›

Yes. Running C is free. Saved snippets may be limited on free accounts; see upgrade messaging if you hit limits.

Which C standard is used?›

The backend uses a common GCC-style toolchain in the sandbox. For strict portability, avoid compiler‑specific extensions unless you verify them.

Can I save my C code?›

Yes, after sign-in. You can reopen from Dashboard → Playground → My Snippets.

Why do I see compile errors?›

Missing semicolons, wrong headers, or invalid types surface as compile errors. Read the message line by line and fix before re-running.

Is this a full IDE?›

No. It is a fast online compiler and playground: single file, run, inspect output. No debugger or multi-file projects yet.

Related languages

Code examples

Tap “Try this” to load sample code into the editor above.

  • Print 1 to n

    #include <stdio.h>

int main(void) {
    int n;
    if (scanf("%d", &n) != 1) return 1;
    for (int i = 1; i <= n; i++) {
        printf("%d\n", i);
    }
    return 0;
}

  • Array sum

    #include <stdio.h>

int main(void) {
    int a[] = {3, 1, 4, 1, 5};
    int sum = 0;
    for (size_t i = 0; i < sizeof(a)/sizeof(a[0]); i++) {
        sum += a[i];
    }
    printf("%d\n", sum);
    return 0;
}

  • String length

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

int main(void) {
    const char *s = "Progsity";
    printf("%zu\n", strlen(s));
    return 0;
}

  • malloc + free

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

int main(void) {
    int *p = (int *)malloc(sizeof(int) * 3);
    if (!p) return 1;
    p[0] = 2; p[1] = 3; p[2] = 5;
    printf("%d\n", p[0] + p[1] + p[2]);
    free(p);
    return 0;
}