What are segmentation faults?

Question

Mnay times I have experienced a problem while executing my c++ codes. The compiler never showed an error during compilation, but half way through the execution, a message "Segementation fault(core dumped)" appeared on the screen.
What actually are these?
Why do they occur?
What can I do to avoid them?

Answer 1

segmentation fault occurs when try to access memory you don't have access to
eg: int a[49];
a[50] = 12; //this causes segmentation fault