A typical function definition looks like this:
1 /* Returns the square of the distance between two points separated by 2 dx in the x direction and dy in the y direction. */ 3 int 4 distSquared(int dx, int dy) 5 { 6 return dx*dx + dy*dy; 7 }
The part outside the braces is called the function declaration; the braces and their contents is the function body.
Like most complex declarations in C, once you delete the type names the declaration looks like how the function is used: the name of the function comes before the parentheses and the arguments inside. The ints scattered about specify the type of the return value of the function (Line 3) and of the parameters (Line 4); these are used by the compiler to determine how to pass values in and out of the function and (usually for more complex types, since numerical types will often convert automatically) to detect type mismatches.
If you want to define a function that doesn't return anything, declare its return type as void. You should also declare a parameter list of void if the function takes no arguments.
1 /* Prints "hi" to stdout */