What are uses of return () statements?

Answer 1

The return statement has only one purpose: to return control back to the calling function.

Although return statements are not required in void functions, return statements can be placed anywhere in any function, void or not. For example:

void f (int x) { // x must be non-zero!

if (!x) return;

// ...

}

In the above example, a precondition is stated in a comment but compilers do not read comments therefore we must test that precondition at runtime. If the precondition fails, then there is no point in continuing any further, so it makes sense to return control to the caller. In a real-world example, we'd set an error condition before returning so that the caller can determine what went wrong.

Note that if we do not put a return statement in a void function, the function automatically returns at the end of the function. This is not the case for functions that return a value; we must explicitly return that value through a return statement. However, we can place the return statement anywhere that is convenient and we can include as many return statements as required. For example:

int g (int x) {

if (!x) return 0;

if (x<=10) return 1;

if (x<=20) return 2;

return 3;

}

In the above example we return the value 0 when x is zero, return 1 when x is in the range 1 to 10, return 2 when x is in the range 11 to 20 and return 3 in all other cases.

The previous example can also be written more succinctly (less verbosely) using the ternary operator:

int g (int x) { return !x ? 0 : (x<=10) ? 1 : (x<=20) ? 2 : 3;

}

However, a good compiler will produce the exact same machine code regardless of how we write the function, therefore it makes sense to use the version that is more readily understood by the reader. After all, code that is easy to understand is generally much easier to maintain.