Online C Debugger — Step Through C Code Visually

What is the Online C Debugger?

The Online C Debugger enables developers and computer science students to step through C code execution line-by-line in real time, inspecting local stack variables, call scopes, and standard output without installing GDB or configuring local toolchains.

Debugging C programs can often feel frustrating because traditional compiler errors only report compile-time issues, while runtime logic errors, off-by-one boundary violations, and pointer dereferences cause silent miscalculations or crashes.

c (ISO Standard)
Run in Compiler.cCopy
#include <stdio.h>

int factorial(int n) {
    if (n <= 1) {
        return 1;
    }
    return n * factorial(n - 1);
}

int main() {
    int num = 5;
    int result = factorial(num);
    printf("Factorial of %d = %d\n", num, result);
    return 0;
}

Key Debugger Features

1. Step-by-Step Execution (Step Over & Step Into)

Step through each instruction sequentially to observe how control flow branches through conditionals, loop iterations, and recursive function calls.

2. Live Variable Watch Window

Inspect how stack variables change state after every single expression. Track integers, floating-point numbers, arrays, and pointer addresses dynamically.

3. Breakpoint Management

Click on any line number in the code editor gutter to set or clear execution breakpoints. Running the program will execute up until the next active breakpoint is reached.

4. Interactive Call Stack

Inspect nested function frames during recursive operations and modular subroutines to understand how stack frames are allocated and deallocated.

Common C Runtime Bugs Detected by Debugging

• Off-by-One Loop Bounds: Iterating past array length (i <= length vs i < length).
• Uninitialized Variable Garbage: Using stack variables before setting their initial values.
• Accidental Assignment in if Statements: Using = instead of == in relational comparisons.
• Dangling Pointers and Memory Leaks: Tracking dynamic memory allocated via malloc() and released with free().

Related Resources & Tools

• Format and indent your source files with our C Code Formatter.
• Detect syntax and linter warnings with our C Syntax Checker.
• Master stack vs heap memory management in the Pointers in C Guide.