#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>
#include <math.h>


int main()
{
   int year1;
   int year2;
   int age;


   printf("Enter year \n");
   scanf(" %d", &year1);


   printf("Enter another year \n");
   scanf(" %d", &year2);


   age = year1 - year2;
   printf("%d \n", age);
   age = abs(age);
   printf("%d \n", age);


   return 0;
}



A few other math functions:


printf("%f \n", pow(5,3) );
printf("%f \n", sqrt(164) );