Convert a number from one base to another

#include<iostream.h>

#include<conio.h>

#include<ctype.h>

#include<process.h>

#include<math.h>

#include<string.h>

class base

{

  private:

          int oldbase,newbase,len,i,j,d,val;

          long dec;

          char oldnum[50],newnum[100];

  public:

          void getdata();

          void getdisp();

};

int value(char dig)

{

           switch (toupper(dig))

          {

                   case'0' : return(0);

                   case'1' : return(1);

                   case'2' : return(2);

                   case'3' : return(3);

                    case'4' : return(4);

                   case'5' : return(5);

                   case'6' : return(6);

                   case'7' : return(7);

                   case'8' : return(8);

                   case'9' : return(9);

                   case'A' : return(10);

                   case'B' : return(11);

                   case'C' : return(12);

                   case'D' : return(13);

                     case'E' : return(14);

                   case'F' : return(15);

                   default:return(-1);

          }

}

char letter(int dig)

{        switch (dig)

          {        case 0: return '0';

                   case 1: return '1';

                   case 2: return '2';

                   case 3: return '3';

                   case 4: return '4';

                   case 5: return '5';

                   case 6: return '6';

                   case 7: return '7';

                   case 8: return '8';

                   case 9: return '9';

                   case 10: return 'A';

                   case 11: return 'B';

                   case 12: return 'C';

                   case 13: return 'D';

                   case 14: return 'E';

                   case 15: return 'F';

                //  default:return'-1';

          }

}

void base::getdata()

{

          cout<<"\n\tBASE CONVERSION\n\n\n";

          cout<<"What is the base of the number to be converted : ";

          cin>>oldbase;

          cout<<"Enter your number : ";

          cin>>oldnum;

          cout<<"What is the new base? : ";

          cin>>newbase;

}

void base::getdisp()

{

          len=strlen(oldnum);

          for(i=len-1,j=0;i>=0;--i,j++)

          {        val=value(oldnum[i]);

                   if((val>oldbase-1)||(val==-1))

                   {        cout<<"Invalid charecter ";

                             getch();

                             exit(1);

                   }

                   dec=dec+pow(oldbase,j)*val;

          }

          for(i=0;dec>0;i++)

          {        d=dec%newbase;

                   newnum[i]=letter(d);

                   dec=dec/newbase;

          }

          newnum[i]='\0';

cout<<"\nNumber "<<oldnum<<" in base "<< oldbase<<" is                     "<<strrev(newnum)<<" in base "<<newbase;

}

void main()

{

          base num;

          clrscr();

          num.getdata();

          num.getdisp();

          getch();

}