Thread: new to programming. help with very simple program

Originally Posted by mehmin

I'm new to programming and just learning the basics. Below I have something to calculate a person's age based on their input using scanf. I don't know if I'm doing something wrong or if codeblocks isn't working. I put in any any number and I get back an answer of -82

Code:

#include <stdio.h>
#include <stdlib.h>
int main()
{
   int age;
   int currentYear;
   int birthYear;


   age = currentYear - birthYear;


   printf("what year is it?\n");
   scanf("%d", ¤tYear);
   printf("what year were you born?\n");
   scanf("%d", &birthYear);
   printf("you are %d years old\n", age);


   return 0;
}

Shouldn't you be calculating age after you get the input from the user, not before you get the input from the user?

The way you wrote the program, there are no values associated with year and birthYear when you calculate age, so the compiler will calculate both of those variables as NULL, and produce a strange output for the age variable. If you calculate age after you get the input from the user, then year and birthYear will have values associated to those variables, and it will calculate age correctly.

Originally Posted by mehmin

Thank you very much for the direction. I suppose I have to think about the process in a more procedural way.

Yes, remember that the values of variables must be stored in memory before any calculations can be made, otherwise the values will be null if nothing is stored in them. Getting input from the user is what gets the values and stores those values in the variables. You have to look at your code as performing one instruction or procedure at a time, so they have to be in order (where your code was out of order).