No defined type of a function parameter defaults to int? Am I insane?

For some odd reason I was copying an example in another language of which does not use types, and forgot to add one in to a function definition parameter, and it worked.

#include <stdio.h>

char toChar(n) {
  //sizeof n is 4 on my 32 bit system
  const char *alpha = "0123456789ABCDEF";
  return alpha[n];
}

int main() {
  putchar(toChar(15)); //i.e.
  return 0;
}

I am sure that main defaults to int by most compilers of some standard (but only return), is this also a behaviour true for other functions as well or is this implementation defined? It seems just out of the ordinary, my compiler is just a slightly outdated GCC port (MinGW).