🔵 GCC C Compiler

Free Online C Compiler

Compile and run C code online using GCC compiler with Monaco editor, pointers support, struct handling, and interactive stdin.

Overview of C Language Compiler

C is the foundational procedural programming language that powers operating systems, embedded hardware, database kernels, and core system tools. Understanding C provides unmatched insight into computer memory management, pointer arithmetic, and system architecture. Our Online C Compiler uses GCC (GNU Compiler Collection) inside an isolated Linux container to compile and execute C source code instantly in your browser. Practice pointers, memory allocation (malloc/free), structs, string manipulation, and Data Structures without installing Code::Blocks, Dev-C++, or local GCC toolchains.

How to Use the C Language Compiler

  1. Type or paste your C source code into the Monaco editor.
  2. Include standard headers like <stdio.h>, <stdlib.h>, or <string.h>.
  3. Provide stdin values if your program uses scanf() or fgets().
  4. Click green ▶ Run Code button to compile via GCC and execute.
  5. Review output, compilation warnings, and execution metrics in the terminal.
  6. Use ✨ Format Code to beautify syntax spacing and alignment.

🧪 Tested Code Examples (C Language)

Example 1: Hello World & Printf Formatting

#include <stdio.h>

int main() {
    printf("Hello, World from Online C Compiler!\n");
    
    int x = 10, y = 20;
    printf("Values: x = %d, y = %d, Sum = %d\n", x, y, x + y);
    return 0;
}
Expected Output: 
Hello, World from Online C Compiler!
Values: x = 10, y = 20, Sum = 30

Code Explanation: The main() function returns 0 upon successful execution. %d format specifiers output integer values.

Example 2: Pointer Arithmetic & Memory Addresses

#include <stdio.h>

int main() {
    int num = 42;
    int *ptr = &num;
    
    printf("Value of num: %d\n", num);
    printf("Address of num: %p\n", (void*)&num);
    printf("Value via ptr: %d\n", *ptr);
    return 0;
}
Expected Output: 
Value of num: 42
Address of num: 0x7ffe...
Value via ptr: 42

Code Explanation: & operator retrieves variable memory address, while * dereferences the pointer to read stored value.

Example 3: Dynamic Memory Allocation (malloc)

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

int main() {
    int n = 5;
    int *arr = (int*)malloc(n * sizeof(int));
    
    if (arr == NULL) {
        printf("Memory allocation failed\n");
        return 1;
    }
    
    for (int i = 0; i < n; i++) {
        arr[i] = (i + 1) * 10;
        printf("arr[%d] = %d\n", i, arr[i]);
    }
    
    free(arr);
    return 0;
}
Expected Output: 
arr[0] = 10
arr[1] = 20
arr[2] = 30
arr[3] = 40
arr[4] = 50

Code Explanation: malloc() allocates dynamic heap memory, checked against NULL. free() deallocates memory post-usage.

💡 Try modifying these examples and execute them directly in the compiler editor above!

🛠️ Common C Language Compiler Errors & Fixes

⚠️ implicit declaration of function

Cause: Calling a function before declaring it or missing required header (e.g. <stdio.h>).

How to Fix: Include appropriate #include <header.h> directives at top of file.

⚠️ segmentation fault (core dumped)

Cause: Dereferencing NULL or invalid pointer, accessing array out of bounds.

How to Fix: Check pointer initialization and array bounds before accessing memory.

⚠️ expected ; before token

Cause: Missing semicolon at end of statement.

How to Fix: Add semicolon ; at end of preceding line statement.

⚠️ conflicting types for function

Cause: Function implementation signature differs from prototype declaration.

How to Fix: Ensure parameter types and return type match prototype exactly.

Frequently Asked Questions (FAQ)

Q: Which GCC compiler version is used?

Our C compiler uses modern GCC on a 64-bit Linux sandbox environment.

Q: Can I use C standard library headers like <stdio.h> and <stdlib.h>?

Yes! Standard C headers including stdio.h, stdlib.h, string.h, math.h, and stdbool.h are fully available.

Q: Does it support scanf() for user input?

Yes, interactive input via scanf(), getchar(), and fgets() is fully supported in our interactive terminal.

Q: Can I test pointers and memory allocation?

Yes! Full support for malloc, calloc, realloc, free, and pointer arithmetic.