Welcome to HCODX Online Compiler
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Compile and run C code online instantly with HCODX. Our free cloud-based C compiler supports real-time execution, standard input, syntax highlighting, and code download. No installation or configuration required. Start coding in C now.
Run C instantly without installing any IDEs or configuring environments. Our cloud-based C handles libraries, runtimes, and dependencies automatically so you can focus on writing code.
Whether you are studying algorithms in C, practicing data structures in C, or exploring functional programming, our tool provides real-time stdout/stderr feedback with interactive standard input support.
HCODX is a free online compiler and code runner: write code in your browser, execute it on a cloud sandbox, and interact with your program through a live terminal. Students use it for coursework and interview practice; developers use it to test snippets in 85+ languages without setting up a local environment.
More than fifty years after Dennis Ritchie created it at Bell Labs, C remains the foundation nearly everything else stands on: the Linux kernel, CPython, SQLite, Git, and most embedded firmware are written in it. Universities still anchor operating-systems and systems-programming courses in C precisely because it hides nothing — pointers, memory layout, and the call stack are yours to manage and yours to break. Your code on this page is compiled with GCC and executed in a live terminal session, which means scanf and fgets read from a real stdin as you type, letting you trace input parsing and pointer behavior without configuring a toolchain.
#include <stdio.h>
#include <string.h>
int main(void) {
char name[64];
int a, b;
printf("Enter your name: ");
scanf("%63s", name);
printf("Enter two integers: ");
scanf("%d %d", &a, &b);
printf("%s, here are your results:\n", name);
printf(" %d + %d = %d\n", a, b, a + b);
printf(" %d * %d = %d\n", a, b, a * b);
printf(" name length = %zu\n", strlen(name));
return 0;
}Work through K&R exercises and systems-course problem sets — string reversal, struct manipulation, manual memory arithmetic — with instant compile feedback, or reproduce a segfault in isolation to understand exactly which pointer went wrong before office hours. Embedded and firmware interview loops still test raw C fluency (bit manipulation, memcpy semantics, undefined behavior traps), and rehearsing those against a real GCC toolchain beats dry-reading a textbook. It's also the fastest way to settle a debate about operator precedence or integer promotion: compile it and see. HCODX is a free online C editor, runner and interpreter — an IDE-grade compiler and playground to write and run code online, execute code with live output and live preview, no downloads or web server required.
Yes — the program runs in a genuine terminal session, so scanf, fgets, and getchar all block until you type. You can even test EOF handling: press Ctrl+D and functions like fgets return NULL exactly as they do in a local Linux terminal, which matters for read-until-end loops.
GCC on Linux, with modern C defaults — so C99 and C11 staples like declarations anywhere in a block, // comments, stdbool.h, and variable-length arrays compile without flags. That mirrors the environment of most university servers and autograders, so code that runs here runs there.
A segfault means your code touched memory it doesn't own — a NULL or uninitialized pointer dereference, writing past an array bound, or returning a pointer to a dead stack variable are the usual suspects. The sandbox surfaces the crash safely, so this is actually a good place to reproduce and minimize one.
Your current code will be replaced with the default sample. This cannot be undone — download your code first if you want to keep it.
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