#include <iostream>
#include <stdlib.h>
#include <string.h>
#include <math.h>
using namespace std;
int main(int argc, char *argv[]){
  //calculate the area of a triangle.
  //command line parameter is angle C(degree). 
  int i=1;
  double a,b,c;
  double A,B,C,S;
  char message[128];
  a=10.0;

  strcpy(message,"input length b >");
  cerr <<"STEP"<< i <<": ";
  cout <<message;
  cin>>b;
  C=atof(argv[1]);
  cout << "a="<<a << " b="<<b<<" C="<<C<<"(degree)"<<endl;
  S=a*b*sin(M_PI*C/180)/2.;
  cout << "area="<<S<<endl;  
  return 0;
}