Variables can be defined inside any block, not just functions.

void main()
{
  int x = 10;
  if (x > 0) {
    int y = 1;
    while (y < 10) {
      int z = 100;
      ...
    }
  }
}

Here, the scope of variable y is the “true” part of if statement and the scope of variable z is the while loop. An automatic variable declared and initialised in a bock is initialised every time the block is entered.

Automatic variables including formal parameters override external variables and functions of the same name. Example:

int x = 10;
float y = 3.4f;

int func(double x)
{
  char y = 'c';
  printf("x = %lf, y = %c\n", x, y);
}

Here, printf will print the value of the parameter x and character ‘c’ corresponding to y.

In practice, it’s best to avoid having the same external and internal names, to prevent any confusion and error.