pointers - C runtime error (undefined behaviour) for performing ++*(p++) on string literal char *p = "abcd"

Question

Question 1:

int main()
{
  char *p="abcd";
  printf("%c",*(p++));
  return 0;
}  // Here it will print a

Question 2:

int main()
{
  char *p="abcd";
  printf("%c",++*(p++));//why it is showing error over here
  return 0;
} // Here it shows runtime error.

Can someone please explain to me why the statement ++*(p++) causes a runtime error.

Answer 1

char *p="abcd";

"abcd" is a string literal and string literals are unmodifiable in C. Attempting to modify a string literal invokes undefined behavior.

Use a modifiable array initialized by a string literal to fix your issue:

char p[] ="abcd";