A function: a. must always have a function prototype even if the function is above main.
b. must have three parameters in the function header.
c. does not need a function prototype if the function itself is above main.
d. always requires a function call, even if you are not using it

a. must always have a function prototype even if the function is above main.

Explanation:

A function must always have a function prototype even if the function is above main.

The function prototype is a declaration which will have to inform the compiler of the function's arguments and the return type. It also tells the computer the name and parameters of function.

This function prototype contains declaration of function and not implementation.

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difference where there's no picture?