what causes segmentation fault in below program [duplicate]

Answer 1

You are allocating a stack variable, the stack of each program is limited.

When you try to allocate too much stack memory, your kernel will kill your program by sending it a SEGV signal, aka segmentation fault.

If you want to allocate bigger chunks of memory, use malloc, this function will get memory from the heap.

Answer 2

Your system must not allow you to make a stack allocation that large. Make matrix global or use dynamic allocation (via malloc and free) and you should be ok.

Answer 3

The matrix is a local variable inside your main function. So it is "allocated" on the machine call stack.

This stack has some limits.

You should make your matrix a global or static variable or make it a pointer and heap-allocate (with e.g. calloc or malloc) the memory zone. Don't forget that calloc or malloc may fail (by returning NULL).

A better reason to heap-allocate such a thing is that the dimensions of the matrix should really be a variable or some input. There are few reasons to wire-in the dimensions in the source code.

Heuristic: don't have a local frame (cumulated sum of local variables' sizes) bigger than a kilobyte or two.

^{[of course, there are valid exceptions to that heuristic]}