We’ve seen how C comes with many handy libraries full of functions for us to use. Now let’s learn how to make our own! To begin, we need a function signature.

The function signature tells us 3 things:

• the function name
• how many parameters (inputs) and their types
• what type of return value is to be expected

returnType functionName (type1 parameter1, type2 parameter2)

If a function isn’t going to return any value, void is used as the return type. void indicates to the compiler that the function returns no data and should not expect to see the return keyword. Any of the types covered in previous lessons, int, char, boolean, etc, can be used as the return type of a function.

Similarly, if a function has no parameters void should be in place of any parameters. The parameters listed inside the parenthesis are like variable declarations. Each parameter should start with the type and then the name of the parameter.

The code statements “inside” the function are known as the body of the function and are enclosed with curly braces after the function signature.

returnType functionName (type1 parameter1, type2 parameter2) {
  // code statement 1;
  // code statement 2;

return output;
}

The signature and the body are the two parts we need to create our own functions.

void makeCookie(){
  printf("Milk\n");
  printf("Flour\n");
  printf("Chocolate Chips\n");
  printf("Butter\n");
  printf("Thanks for the ingredients, here's a cookie!\n");
}