Fix 'Segmentation Fault' in Online C Compiler

🧠 What is a Segmentation Fault in C?

A segmentation fault occurs when a program tries to access a memory area it shouldn't — for example, dereferencing an invalid pointer or accessing memory out of bounds.

🚨 Common Causes in Online C Compilers (and Fixes)

✅ 1. Uninitialized or NULL Pointer Dereference

int *ptr; *ptr = 10; // ❌ Segmentation Fault

Fix:

int *ptr = (int *)malloc(sizeof(int)); *ptr = 10; printf("%dn", *ptr); free(ptr);

✅ 2. Array Index Out of Bounds

int arr[5]; arr[10] = 100; // ❌ Invalid memory access

Fix:

int arr[5]; arr[4] = 100; // ✅ Within valid range

✅ 3. Improper Use of scanf()

int num; scanf("%d", num); // ❌ Segmentation fault

Fix:

int num; scanf("%d", &num); // ✅ Correct usage

✅ 4. Using Freed Memory

int *ptr = malloc(sizeof(int)); free(ptr); *ptr = 5; // ❌ Illegal memory access

Fix: Avoid using ptr after freeing it, or set it to NULL.

✅ 5. Stack Overflow (Deep Recursion)

void recurse() { recurse(); // ❌ No base case leads to stack overflow }

Fix:

void recurse(int count) { if (count <= 0) return; recurse(count - 1); }

🛠️ How to Debug in Online C Compiler

• Add printf() statements to check variable values.
• Isolate the faulty block and test separately.
• Use tools like Online C Compiler with input/output preview.
• Avoid dynamic memory usage unless necessary.

💡 Pro Tip

Always initialize pointers and arrays properly, and double-check loops and input handling when using online compilers — they are more sensitive to runtime crashes due to limited memory.

✅ Conclusion

Segmentation faults are common, especially in C. But with careful pointer handling, bounds checking, and input validation, you can easily avoid them — even on an online compiler.