C++ Programming

# include <conio.h>
# include <iostream.h>
# include <math.h>

main()
{

int der,FN,LN,I;
float rad,s,c,t;

clrscr();
cout <<"\n******************************************";
cout <<"\n*  TRIGONOMETRY ANGEL NUMBERING PROGRAM  *";
cout <<"\n******************************************";
cout <<"\n\n";
cout <<"Enter first number !   = "; cin >>FN;
cout <<"Enter last number !  = "; cin >>LN;
cout <<"Enter interval !     = "; cin >>I;
cout <<"\n\n";
cout <<"\n=================================================";
cout <<"\n|DERAJAT| RADIAN  |  SINUS  | COSINUS | TANGEN  |";
cout <<"\n=================================================";

if(LN<FN)
{
cout <<"\n\t~~~~~~~~~~~~EEEEERRRROOOORRRRR~~~~~~~~~~~~";
cout <<"\nYour false entering first number or last number";
}
else
{
for(der=FN;der<=LN;der=der+I)
{
rad=1;

rad=M_PI/180*der;
s=sin(rad);
c=cos(rad);
t=tan(rad);
cout <<"\n|  "<<der<<"  | "<<rad<<" | " <<s<< " | " <<c<< " | " <<t<< " |";
cout <<"\n===================================================";
}
}
cout <<"\n\n\n";
cout <<"\t~~~~~~~~~~~~THANK YOU~~~~~~~~~~~~";

getch();
}