3.11. Functions with Results¶

You might have noticed by now that some of the functions we are using, like the math functions, yield results. Other functions, like newLine, perform an action but don’t return a value. That raises some questions:

What happens if you call a function and you don’t do anything with the result (i.e. you don’t assign it to a variable or use it as part of a larger expression)?
What happens if you use a function without a result as part of an expression, like newLine() + 7?
Can we write functions that yield results, or are we stuck with things like newLine and printTwice?

The answer to the third question is “yes, you can write functions that return values,” and we’ll do it in a couple of chapters. I will leave it up to you to answer the other two questions by trying them out.

Note

Any time you have a question about what is legal or illegal in C++, a good way to find out is to ask the compiler. It will let you answer your question by throwing an error… or not!

Q-1: What will be printed when the following code runs?

#include <iostream>
using namespace std;

void multiply (int x, int y) {
  cout << x*y;
}

int main() {
  int x = 2;
  int y = 4;
  multiply(x,y);
}

Q-2: Will the following code compile?

#include <iostream>
using namespace std;

void multiply (int x, int y) {
  cout << x * y << endl;
}

int main() {
  int x = 2;
  int y = 4;
  cout << multiply(x,y);
}

Yes
Can you print the result of a void function?
No
Correct! You can’t print the result of a void function