Welcome to XCODX Online Compiler
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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.
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.
main.ctext/x-csrcscanf() / fgets()#include <stdio.h>
int main() {
printf("Hello from C!\n");
printf("Welcome to XCODX Online Compiler!\n");
return 0;
}