Thread: Function to return user input in C

Firstly, I'd like to say that I'm relatively new to functions and my course standards state that I'm now supposed to relay information from the user to the program via functions, this means that I'm no longer able to use 'printf/scanf' combos in the main function.

Is it possible to do it via functions? I've tried the following method for example, but to no avail. It's confusing me.

Code:

#include <stdio.h>

int getlowR();




int main(void)
{

  getlowR();


  printf("Low range: %d, High range: %d", lowRange);


  return(0);
}

int getlowR()
{
  int lowRange;

  printf("Enter the low range value:");
  scanf("%d", &lowRange);
  return(lowRange);
}

I think the following works but then lowRange is native to the function, isn't it? How can I use it outside the function? For example, how would I go about actually printing the value acquired by the function in main?

Thanks.

Essentially, getlowR() returns an integer that you can assign to a variable in main(). Ie.

Code:

int a = getlowR();

The longer explanation is twofold:
1. The variables declared in a function (e.g. lowRange) are local to that function - which means lowRange doesn't exist in main(), nor can main see it.
2. To understand any expression, you can evaluate all the operands in the expression by substitution. For non-void functions, this means substitute the function call with the value that the function returns.
So as an example, let's say getlowR() returns the integer 5. Then in main() we substitute the function call with 5. Then you have the statement

Code:

  5;

which as you can see is meaningless. So the gist of it is, that functions that return values can be used in any expression that is valid for that return type.

It should be clear that void functions don't return values and therefore shouldn't be used in expressions.

That's a good question. Sometimes you don't need local storage for the value you're returning. In your case, scanf requires someplace to store the value read, so there's no getting around that.

But assume a and b are integers and foo() is a another function. We can return expressions directly using a, b, and foo().

Code:

return a + b  ;
////////////////
return 2*a + 3*b ;
///////////////
return a < b;            //This takes advantage that the expression a < b evaluates to 1 if true, 0 if false.
//////////////
return a + foo( a, b );     //Here we call foo with a and b as arguments, and we will return the sum of a and the value that foo returns

Hope that gives you some ideas.

Thanks a lot, you've been a great help. I'll practice some more tomorrow.