hero.c

#include <stdio.h> 
#include <math.h> 

double hero(double a,double b,double c){ 
  double s,T; 
  if(a+b<c || b+c<a || c+a<b){ 
    return -1; 
  }else{ 
    s=(a+b+c)/2; 
    T=sqrt(s*(s-a)*(s-b)*(s-c)); 
    return T; 
  }  
} 
int main(void){
  double a,b,c, area;
  printf("a = ");
  scanf("%lf", &a);
  printf("b = ");
  scanf("%lf", &b);
  printf("c = ");
  scanf("%lf", &c);
  if((area = hero(a,b,c)) != -1){
    printf("T = %lf\n", area);
  }else{
    printf("三角形の入力が間違っています。");
  }
  return 0;
}