Why does omitting explicit 'int' type for a parameter fail to compile in gcc sometimes?

Question

When declaring variables in C you can omit the type sometimes if you want to declare an int.

Why does omitting explicit \'int\' type for a parameter fai

Answer 1

The compiler is employing one of two grammars.

When applying the K&R grammar, undeclared parameters are allowed, and default to ints.

When applying the non-K&R grammar, all parameters must comply with the parameter declaration syntax i.e. declared with types and names.

You invoke one or the other by choosing the corresponding declaration style.