24.3 Argument Promotions

When a function’s definition or declaration does not specify the type of an argument, that argument is passed without conversion in whatever type it has, with these exceptions:

• Some narrow numeric values are promoted to a wider type. If the expression is a narrow integer, such as char or short, the call converts it automatically to int (see Integer Types).⁸

  In this example, the expression c is passed as an int:

  char c = '$';
  
  printf ("Character c is '%c'\n", c);
  

• If the expression has type float, the call converts it automatically to double.
• An array as argument is converted to a pointer to its zeroth element.
• A function name as argument is converted to a pointer to that function.