Those are old K&R style function parameter declarations, declaring the types of the parameters separately:
int func(a, b, c)
int a;
int b;
int c;
{
return a + b + c;
}
This is the same as the more modern way to declare function parameters:
int func(int a, int b, int c)
{
return a + b + c;
}
The “new style” declarations are basically universally preferred.