/*
 * triangle.c -- triangle classification program
 *
 * To build: gcc -o triangle triangle.c
 *
 */

#include <stdio.h>
#include <stdlib.h>

int main(int argc, const char *argv[])
{
   int a, b, c, d;
   
   if ( argc < 4 )
   {
      printf("Usage: %s length1 length2 length3\n", argv[0]);
      printf("  List lengths in descending order.\n");
      return 1;
   }

   a = atoi(argv[1]);
   b = atoi(argv[2]);
   c = atoi(argv[3]);

   if ( a <= 0 || b <= 0 || c <= 0 )
   {
      printf("Illegal side lengths.\n");
      exit(1);
   }
   
   printf("Sides with length %d, %d, and %d", a, b, c);
   
   if ( a >= b && b >= c && a + b > c && a + c > b && b + c > a )
   {
      if ( a == b || b == c )
      {
         if ( a == b && b == c )
         {
            printf(" form an equilateral triangle.\n");
         }
         else
         {
            printf(" form an isosceles triangle.\n");
         }
      }    
      else
      {
         a = a * a;
         b = b * b;
         c = c * c;
         d = b + c;
         if ( a != d )
         {
            if ( a < d )
               printf(" form an obtuse triangle.\n");
            else
               printf(" form an acute triangle.\n");
         }
         else
         {
            printf(" form a right triangle.\n");
         }
      }
   }
   else
   {
      if ( a < b || b < c )
         printf(" are not descending.\n");
      else
         printf(" cannot form a triangle.\n");
   }
   
   return 0;
}