# include <iostream.h>
 # include <string.h>
 # include <stdlib.h>
 # include <conio.h>
 # include <ctype.h>
 # include <math.h>
 # include <dos.h>

 constint max_size=30;
 constint table_size=12;

 int top=-1;
 int n=0;
 int order=0;
 int input_choice=0;

 longdouble x0=0;
 longdouble difference=0;

 longdouble x_values[table_size]={0};
 longdouble difference_table[table_size][table_size]={0};

 char Non_linear_equation[100]={NULL};
 char Stack[max_size][max_size]={NULL};
 char Postfix_expression[max_size][max_size]={NULL};


 void push(constchar *);
 void convert_infix_expression_to_postfix_expression(constchar *);

 constchar* pop( );
 constlongdouble evaluate_postfix_expression(constlongdouble);

 void show_screen( );
 void clear_screen( );
 void get_input_mode( );
 void get_input_non_linear_equation( );
 void get_input_table( );
 void construct_difference_table( );
 void show_difference_table( );
 void compute_and_display_difference_operators( );


 int main( )
    {
       clrscr( );
       textmode(C4350);

       show_screen( );
       get_input_mode( );
       construct_difference_table( );
       show_difference_table( );
       compute_and_display_difference_operators( );

       return 0;
    }

  /*************************************************************************///--------------------------  push(const char*)  ------------------------///*************************************************************************/void push(constchar* Operand)
    {
       if(top==(max_size-1))
      {
         cout<<"Error : Stack is full."<<endl;
         cout<<"\n        Press any key to exit.";

         getch( );
         exit(0);
      }

       else
      {
         top++;
         strcpy(Stack[top],Operand);
      }
    }

 /*************************************************************************///------------------------------  pop( )  -------------------------------///*************************************************************************/constchar* pop( )
    {
       char Operand[40]={NULL};

       if(top==-1)
      {
         cout<<"Error : Stack is empty."<<endl;
         cout<<"\n        Press any key to exit.";

         getch( );
         exit(0);
      }

       else
      {
         strcpy(Operand,Stack[top]);
         strset(Stack[top],NULL);
         top--;
      }

       return Operand;
    }

 /*************************************************************************///----  convert_infix_expression_to_postfix_expression(const char*)  ----///*************************************************************************/void convert_infix_expression_to_postfix_expression(constchar* Expression)
    {
       char Infix_expression[100]={NULL};
       char Symbol_scanned[30]={NULL};

       push("(");
       strcpy(Infix_expression,Expression);
       strcat(Infix_expression,"+0)");

       int flag=0;
       int count_1=0;
       int count_2=0;
       int equation_length=strlen(Infix_expression);

       if(Infix_expression[0]=='(')
      flag=1;

       do
      {
         strset(Symbol_scanned,NULL);

         if(flag==0)
        {
           int count_3=0;

           do
              {
             Symbol_scanned[count_3]=Infix_expression[count_1];

             count_1++;
             count_3++;
              }
           while(count_1<=equation_length &&
               Infix_expression[count_1]!='(' &&
                  Infix_expression[count_1]!='+' &&
                 Infix_expression[count_1]!='-' &&
                    Infix_expression[count_1]!='*' &&
                       Infix_expression[count_1]!='/' &&
                      Infix_expression[count_1]!='^' &&
                         Infix_expression[count_1]!=')');


           flag=1;
        }

         elseif(flag==1)
        {
           Symbol_scanned[0]=Infix_expression[count_1];

           count_1++;

           if(Infix_expression[count_1]!='(' &&
             Infix_expression[count_1]!='^' &&
                Infix_expression[count_1]!='*' &&
                   Infix_expression[count_1]!='/' &&
                  Infix_expression[count_1]!='+' &&
                     Infix_expression[count_1]!='-' &&
                    Infix_expression[count_1]!=')')
              flag=0;

           if(Infix_expression[count_1-1]=='(' &&
               (Infix_expression[count_1]=='-' ||
                 Infix_expression[count_1]=='+'))
              flag=0;
        }

         if(strcmp(Symbol_scanned,"(")==0)
        push("(");

         elseif(strcmp(Symbol_scanned,")")==0)
        {
           while(strcmp(Stack[top],"(")!=0)
              {
             strcpy(Postfix_expression[count_2],pop( ));

             count_2++;
              }

           pop( );
        }

         elseif(strcmp(Symbol_scanned,"^")==0 ||
               strcmp(Symbol_scanned,"+")==0 ||
                 strcmp(Symbol_scanned,"-")==0 ||
                       strcmp(Symbol_scanned,"*")==0 ||
                         strcmp(Symbol_scanned,"/")==0)
        {
           if(strcmp(Symbol_scanned,"^")==0)
              {  }

           elseif(strcmp(Symbol_scanned,"*")==0 ||
                          strcmp(Symbol_scanned,"/")==0)
              {
             while(strcmp(Stack[top],"^")==0 ||
                     strcmp(Stack[top],"*")==0 ||
                       strcmp(Stack[top],"/")==0)
                {
                   strcpy(Postfix_expression[count_2],pop( ));

                   count_2++;
                }
              }

           elseif(strcmp(Symbol_scanned,"+")==0 ||
                    strcmp(Symbol_scanned,"-")==0)
              {
             while(strcmp(Stack[top],"(")!=0)
                {
                   strcpy(Postfix_expression[count_2],pop( ));

                   count_2++;
                }
              }

           push(Symbol_scanned);
        }

         else
        {
           strcat(Postfix_expression[count_2],Symbol_scanned);

           count_2++;
        }
      }
       while(strcmp(Stack[top],NULL)!=0);

       strcat(Postfix_expression[count_2],"=");
       count_2++;
    }

 /*************************************************************************///---------  evaluate_postfix_expression(const long double)  ------------///*************************************************************************/constlongdouble evaluate_postfix_expression(constlongdouble x)
    {
       longdouble function_value=0;

       int count_1=-1;

       char Symbol_scanned[30]={NULL};

       do
      {
         count_1++;

         strcpy(Symbol_scanned,Postfix_expression[count_1]);

         if(strcmp(Symbol_scanned,"^")==0 ||
              strcmp(Symbol_scanned,"*")==0 ||
                strcmp(Symbol_scanned,"/")==0 ||
                  strcmp(Symbol_scanned,"+")==0 ||
                    strcmp(Symbol_scanned,"-")==0)

        {
           char Result[30]={NULL};
           char Operand[2][30]={NULL};

           strcpy(Operand[0],pop( ));
           strcpy(Operand[1],pop( ));

           longdouble operand[2]={0};
           longdouble result=0;

           char *endptr;

           for(int count_2=0;count_2<2;count_2++)
              {
             int flag=0;

             if(Operand[count_2][0]=='-')
                {
                   int length=strlen(Operand[count_2]);

                   for(int count_3=0;count_3<(length-1);count_3++)
                  Operand[count_2][count_3]=Operand[count_2][(count_3+1)];

                   Operand[count_2][count_3]=NULL;

                   flag=1;
                }

             if(strcmp(Operand[count_2],"x")==0)
                operand[count_2]=x;

             elseif(strcmp(Operand[count_2],"e")==0)
                operand[count_2]=2.718282;

             elseif(strcmp(Operand[count_2],"sinx")==0)
                operand[count_2]=sinl(x);

             elseif(strcmp(Operand[count_2],"cosx")==0)
                operand[count_2]=cosl(x);

             elseif(strcmp(Operand[count_2],"tanx")==0)
                operand[count_2]=tanl(x);

             elseif(strcmp(Operand[count_2],"lnx")==0)
                operand[count_2]=logl(x);

             elseif(strcmp(Operand[count_2],"logx")==0)
                operand[count_2]=log10l(x);

             else
                operand[count_2]=strtod(Operand[count_2],&endptr);

             if(flag)
                operand[count_2]*=-1;
              }

           switch(Symbol_scanned[0])
              {
             case'^' : result=powl(operand[1],operand[0]);
                    break;

             case'*' : result=operand[1]*operand[0];
                    break;

             case'/' : result=operand[1]/operand[0];
                    break;

             case'+' : result=operand[1]+operand[0];
                    break;

             case'-' : result=operand[1]-operand[0];
                    break;
              }

           gcvt(result,25,Result);

           push(Result);
        }

         elseif(strcmp(Symbol_scanned,"=")!=0)
        push(Symbol_scanned);
      }
       while(strcmp(Symbol_scanned,"=")!=0);

       char Function_value[30]={NULL};
       char *endptr;

       strcpy(Function_value,pop( ));
       function_value=strtod(Function_value,&endptr);

       return function_value;
    }

 /*************************************************************************///--------------------------  show_screen( )  ---------------------------///*************************************************************************/void show_screen( )
    {
       cprintf("\n********************************************************************************");
       cprintf("****************************-                      -****************************");
       cprintf("*---------------------------- ");

       textbackground(1);
       cprintf(" Finite-Differences ");
       textbackground(8);

       cprintf(" ----------------------------*");
       cprintf("****************************-                      -****************************");
       cprintf("********************************************************************************");

       for(int count=0;count<42;count++)
      cprintf("*                                                                              *");

       gotoxy(1,46);
       cprintf("********************************************************************************");
       cprintf("*------------------------------------------------------------------------------*");
       cprintf("********************************************************************************");

       gotoxy(1,2);
    }

 /*************************************************************************///-------------------------  clear_screen( )  ---------------------------///*************************************************************************/void clear_screen( )
    {
       for(int count=0;count<37;count++)
      {
         gotoxy(3,8+count);
         cout<<"                                                                            ";
      }

       gotoxy(1,2);
    }

 /*************************************************************************///-------------------------  get_input_mode( )  -------------------------///*************************************************************************/void get_input_mode( )
    {
       gotoxy(4,11);
       cout<<"Input Mode :";

       gotoxy(4,12);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(8,15);
       cout<<"a)-  Press `1' to enter a function f(x).";

       gotoxy(8,18);
       cout<<"b)-  Press `2' to enter values of the function.";

       do
      {
         gotoxy(8,25);
         cout<<"Enter your choice =    ";
         gotoxy(28,25);

         input_choice=(int(getche( ))-48);

         if(input_choice!=1 && input_choice!=2)
        {
           sound(2500);
           delay(500);
           nosound( );
        }
      }
       while(input_choice!=1 && input_choice!=2);

       if(input_choice==1)
      get_input_non_linear_equation( );

       elseif(input_choice==2)
      get_input_table( );

       gotoxy(1,2);
    }

 /*************************************************************************///------------------  get_input_non_linear_equation( )  -----------------///*************************************************************************/void get_input_non_linear_equation( )
    {
       clear_screen( );

       gotoxy(4,11);
       cout<<"Non-Linear Function with One Variable:";

       gotoxy(4,12);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(6,37);
       cout<<"Note : Write the function with proper Braces ( ) e.g; 2x+3 as (2*x)+3";

       gotoxy(6,40);
       cout<<"Available Operators  :  ^ (raised to power) , * , / , + , -";

       gotoxy(6,42);
       cout<<"Available Operands   :  x , e , sinx , cosx , tanx , lnx , logx ,";

       gotoxy(6,44);
       cout<<"                        n = any number";

       gotoxy(4,15);
       cout<<"Enter the Function = f(x) = ";
       cin>>Non_linear_equation;

       gotoxy(4,20);
       cout<<"Enter the initial value of x = x0 = ";
       cin>>x0;

       gotoxy(4,23);
       cout<<"Enter the interval b/w two points = ";
       cin>>difference;

       gotoxy(4,28);
       cout<<"                       [ Max. n = 12 ] ";

       gotoxy(4,26);
       cout<<"Enter the total number of values = n =  ";
       cin>>n;

       if(n>12)
      n=12;

       convert_infix_expression_to_postfix_expression(Non_linear_equation);

       longdouble x=x0;

       for(int count_1=0;count_1<n;count_1++)
      {
         difference_table[0][count_1]=evaluate_postfix_expression(x);
         x_values[count_1]=x;

         x+=difference;
      }

       gotoxy(1,2);
    }

 /*************************************************************************///--------------------------  get_input_table( )  -----------------------///*************************************************************************/void get_input_table( )
    {
       clear_screen( );

       gotoxy(4,9);
       cout<<"Table of Values for Function :";

       gotoxy(4,10);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(4,14);
       cout<<"                       [ Max. n = 12 ]";

       gotoxy(4,12);
       cout<<"Enter the total number of values = n = ";
       cin>>n;

       if(n>12)
      n=12;

       gotoxy(4,16);
       cout<<"Enter the initial value of x = x0 = ";
       cin>>x0;

       gotoxy(4,18);
       cout<<"Enter the interval b/w two points = ";
       cin>>difference;

       double x=x0;

       for(int count_1=0;count_1<n;count_1++)
      {
         x_values[count_1]=x;

         x+=difference;
      }

       int x_cord=45;
       int y_cord=19;

       gotoxy(x_cord,(y_cord-4));
       cout<<"ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿";

       gotoxy(x_cord,(y_cord-3));
       cout<<"³      Xi       ³    f(Xi)      ³";

       gotoxy(x_cord,(y_cord-2));
       cout<<"ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ´";

       gotoxy(x_cord,(y_cord-1));
       cout<<"³               ³               ³";

       gotoxy(x_cord,y_cord);
       cout<<"³               ³               ³";

       for(int count_2=0;count_2<n;count_2++)
      {
         gotoxy(x_cord,(y_cord+1));
         cout<<"³               ³               ³";

         gotoxy(x_cord,(y_cord+2));
         cout<<"³               ³               ³";

         y_cord+=2;
      }

       gotoxy(x_cord,y_cord);
       cout<<"ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ";

       y_cord=19;

       for(int count_3=0;count_3<n;count_3++)
      {
         gotoxy((x_cord+2),y_cord);
         cout<<x_values[count_3];

         gotoxy((x_cord+18),y_cord);
         cin>>difference_table[0][count_3];

         y_cord+=2;
      }

       gotoxy(1,2);
    }

 /*************************************************************************///-------------------  construct_difference_table( )  -------------------///*************************************************************************/void construct_difference_table( )
    {
       int flag=0;

       for(int count_1=1;count_1<n;count_1++)
      {
         for(int count_2=count_1;count_2<n;count_2++)
        {
           longdouble fx1=difference_table[(count_1-1)][(count_2-1)];
           longdouble fx2=difference_table[(count_1-1)][count_2];

           difference_table[count_1][count_2]=fx2-fx1;
        }

         flag=1;

         for(int count_3=count_1;count_3<n;count_3++)
        {
           if(difference_table[count_1][count_3]!=0)
              {
             flag=0;

             break;
              }
        }

         if(flag)
        {
           order=count_1;

           break;
        }
      }

       if(count_1==n)
      order=(n-1);
    }

 /*************************************************************************///----------------------  show_difference_table( )  ---------------------///*************************************************************************/void show_difference_table( )
    {
       clear_screen( );

       gotoxy(4,10);
       cout<<"Difference Table :";

       gotoxy(4,11);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(4,13);
       cout<<"ÚÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

       gotoxy(4,14);
       cout<<"³   x    ³     f(x)      ";

       gotoxy(4,15);
       cout<<"ÃÄÄÄÄÄÄÄÄÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

       gotoxy(4,16);
       cout<<"³        ³               ";

       int x_cord=4;
       int y_cord=17;

       for(int count_1=0;count_1<n;count_1++)
      {
         gotoxy(x_cord,y_cord);
         cout<<"³        ³               ";

         gotoxy(x_cord,(y_cord+1));
         cout<<"³        ³               ";

         gotoxy((x_cord+2),y_cord);
         cout<<x_values[count_1];

         gotoxy((x_cord+11),y_cord);
         cout<<difference_table[0][count_1];

         y_cord+=2;
      }

       gotoxy(x_cord,y_cord);
       cout<<"ÀÄÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

       x_cord+=20;

       int count_2=0;

       for(int count_3=1;count_3<=order;count_3++)
      {
         gotoxy(x_cord,13);
         cout<<"ÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

         gotoxy(x_cord,14);
         cout<<"³";

         gotoxy(x_cord,15);
         cout<<"ÅÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

         gotoxy(x_cord,16);
         cout<<"³";

         gotoxy(x_cord,y_cord);
         cout<<"ÁÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ";

         gotoxy((x_cord+6),14);
         cout<<count_3;

         if(count_3==1)
        cout<<"st";

         elseif(count_3==2)
        cout<<"nd";

         elseif(count_3==3)
        cout<<"rd";

         else
        cout<<"th";

         y_cord=17;

         for(int count_4=0;count_4<n;count_4++)
        {
           gotoxy(x_cord,y_cord);
           cout<<"³";

           gotoxy(x_cord,(y_cord+1));
           cout<<"³";

           if(count_4>=count_3)
              {
             gotoxy((x_cord+2),(y_cord-count_3));
             cout<<difference_table[count_3][count_4];
              }

           y_cord+=2;
        }

         x_cord+=16;
         count_2++;

         if((count_2%3)==0 && count_3<order)
        {
           gotoxy(x_cord,13);
           cout<<"ÂÄÄ";

           gotoxy(x_cord,14);
           cout<<"³";

           gotoxy(x_cord,15);
           cout<<"ÅÄÄ";

           gotoxy(x_cord,16);
           cout<<"³";

           gotoxy(x_cord,y_cord);
           cout<<"ÁÄÄ";

           y_cord=17;

           for(int count_5=0;count_5<n;count_5++)
              {
             gotoxy(x_cord,y_cord);
             cout<<"³";

             gotoxy(x_cord,(y_cord+1));
             cout<<"³";

             y_cord+=2;
              }

           gotoxy(30,44);
           cout<<"Press any key to continue...";
           getch( );

           y_cord=13;
           x_cord=24;

           for(int count_6=0;count_6<=(n+2);count_6++)
              {
             gotoxy(x_cord,y_cord);
             cout<<"                                                       ";

             gotoxy(x_cord,(y_cord+1));
             cout<<"                                                       ";

             y_cord+=2;
              }

           y_cord-=2;
           count_2=0;
           count_3--;
        }
      }

       gotoxy(x_cord,13);
       cout<<"¿";

       gotoxy(x_cord,14);
       cout<<"³";

       gotoxy(x_cord,16);
       cout<<"³";

       y_cord=17;

       for(int count_6=0;count_6<n;count_6++)
      {
         gotoxy(x_cord,y_cord);
         cout<<"³";

         gotoxy(x_cord,(y_cord+1));
         cout<<"³";

         y_cord+=2;
      }

       gotoxy(x_cord,15);
       cout<<"´";

       gotoxy(x_cord,y_cord);
       cout<<"Ù";

       gotoxy(30,44);
       cout<<"Press any key to continue...";

       getch( );
    }

 /*************************************************************************///-----------  compute_and_display_difference_operators( )  -------------///*************************************************************************/void compute_and_display_difference_operators( )
    {
       clear_screen( );

       gotoxy(6,10);
       cout<<"Difference Operators :";

       gotoxy(6,11);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(10,13);
       cout<<"E  =  Shift Operator";

       gotoxy(10,15);
       cout<<"D  =  Forward Difference Operator";

       gotoxy(10,17);
       cout<<"d  =  Backward Difference Operator";

       gotoxy(6,20);
       cout<<"Examples :";

       gotoxy(6,21);
       cout<<"ÍÍÍÍÍÍÍÍÍÍ";

       gotoxy(10,23);
       cout<<"Shift Operator :  Ef2 , E3f4 , E3f1";

       gotoxy(10,25);
       cout<<"Forward Difference Operator : Df3 , D2f1 , D3f0";

       gotoxy(10,27);
       cout<<"Backward Difference Operator : df3 , d2f3 , d4f4";

       gotoxy(6,44);
       cout<<"Note :  Enter `0' to exit, `V' to view Difference Table again.";

       gotoxy(6,32);
       cout<<"Calculate ?";

       gotoxy(6,33);
       cout<<"ÍÍÍÍÍÍÍÍÍÍÍ";

       char Operator[10]={NULL};
       longdoublevalue=0;

       do
      {
         strset(Operator,NULL);

         value=0;

         gotoxy(10,35);
         cout<<"                                                   ";

         gotoxy(10,37);
         cout<<"                                                  ";

         gotoxy(10,40);
         cout<<"                                                  ";

         gotoxy(10,35);
         cout<<"Operator  =  ";
         cin>>Operator;

         if(strcmp(Operator,"v")==0 || strcmp(Operator,"V")==0)
        {
           show_difference_table( );
           compute_and_display_difference_operators( );
        }

         elseif(strcmp(Operator,"0")!=0)
        {
           if(Operator[0]=='E' || Operator[0]=='D' ||
                              Operator[0]=='d')
              {
             int flag=0;

             if(strchr(Operator,'f')==NULL)
                flag=1;

             if(Operator[0]=='E' && !flag)
                {
                   int fn=1;

                   char Temp[10]={NULL};

                   if(isdigit(Operator[1]))
                  {
                     strcpy(Temp,strtok(Operator,"E"));
                     strcpy(Temp,strtok(Temp,"f"));
                  }

                   fn=atoi(Temp);

                   if(strcmp(Temp,NULL)==0)
                  fn=1;

                   strset(Temp,NULL);

                   strtok(Operator,"f");

                   strcpy(Temp,strtok(NULL,NULL));

                   fn+=atoi(Temp);

                   if(fn>(n-1) || fn<0)
                  flag=1;

                   value=difference_table[0][fn];
                }

             elseif(Operator[0]=='D' && !flag)
                {
                   int D=1;
                   int f=0;

                   char Temp[10]={NULL};

                   if(isdigit(Operator[1]))
                  {
                     strcpy(Temp,strtok(Operator,"D"));
                     strcpy(Temp,strtok(Temp,"f"));
                  }

                   D=atoi(Temp);

                   if(strcmp(Temp,NULL)==0)
                  D=1;

                   strset(Temp,NULL);

                   strtok(Operator,"f");

                   strcpy(Temp,strtok(NULL,NULL));

                   f=atoi(Temp);

                   if(D>(n-1) || D<=0 || (D+f)>(n-1) || D<0)
                  flag=1;

                   value=difference_table[D][(D+f)];
                }

             elseif(Operator[0]=='d' && !flag)
                {
                   int d=1;
                   int f=0;

                   char Temp[10]={NULL};

                   if(isdigit(Operator[1]))
                  {
                     strcpy(Temp,strtok(Operator,"d"));
                     strcpy(Temp,strtok(Temp,"f"));
                  }

                   d=atoi(Temp);

                   if(strcmp(Temp,NULL)==0)
                  d=1;

                   strset(Temp,NULL);

                   strtok(Operator,"f");

                   strcpy(Temp,strtok(NULL,NULL));

                   f=atoi(Temp);

                   if(d>(n-1) || d<=0 || f<d || f>(n-1))
                  flag=1;

                   value=difference_table[d][f];
                }

             if(!flag)
                {
                   gotoxy(10,37);
                   cout<<"Value  =  "<<value;

                   gotoxy(25,40);
                   cout<<"Press any key to continue...";
                }

             else
                {
                   gotoxy(25,40);
                   cout<<"Wrong Values. Try again...";
                }
              }

           else
              {
             gotoxy(25,40);
             cout<<"Wrong Operator. Try again...";
              }

           getch( );
        }

         elseif(strcmp(Operator,"0")==0)
        {
           gotoxy(1,2);

           delay(500);
           exit(0);
        }
      }
       while(1);
    }