C Programming Absolute Beginner's Guide (3rd Edition)

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sales = quantity * price;

return (sales);

is identical to this:

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return (quantity * price);

The return Data Type

At the beginning of the gradeAve() function, you see float. float is the data type of the
returned value localAverage. You must put the return data type before any function name that
returns a value. If the function returned a long int, long int would have to precede the
function name.

If you don’t specify a return data type, C assumes int. Therefore, C expects that every function
without a return data type specified explicitly will return int. Both of these functions’ first lines
mean exactly the same thing to C:

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int myFun(int a, float x, char c)

and

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myFun(int a, float x, char c) /* int is assumed */

Tip

Guess what? Even main() is assumed to return an int value unless you specify an

overriding return data type. That is why you’ve seen return 0; at the end of most

of these programs! Because main() has no specified return data type, int is

assumed, and the return 0; ensures that an int is returned to your operating

system.

If your function doesn’t return a value, or if your function isn’t passed a value, you can insert the
keyword void for either the return data type or the parameter list or both. Therefore, the first line of
a function that neither gets any value nor returns any value might look like this:

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void doSomething(void) /* Neither is passed nor returns */

Warning

main() can’t be of type void if you use strict American National Standards Institute