Add Subtract Multiply Divide Modulo m+ m- mc Calculator Program in C++

#include<iostream.h>
#include<stdlib.h>
#include<math.h>
double memory=0;
double add (double x)
{
double y;
cout<<"\n\n number:";
cin>>y;
cout<<"\n";
return (x+y);
}
double multiply(double x)
{
double y;
cout<<"\n\n number:";
cin>>y;
cout<<"\n";
cout<<x<<"*"<<y<<"=";
return(x*y);
}
double substract(double x)
{
double y;
cout<<"\n\n number:";
cin>>y;
cout<<"\n";
return(x-y);
}
double divide(double x)
{
double y;
cout <<"\n\nnumber:";
cin>>y;
cout <<"\n";
return (x/y);
}
double modulo(double x)
{
double y;
cout<<"\n\n number:";
cin>>y;
cout <<"\n";
if((int)x-x!=0 !! (int)y-y!=0)
throw1;
return((int)x%(int)y);
}
int main()
{
double firstnumber;
double secondnumber;
int operand;
void calculator(double firstnumber);
system("CLS");
cout<<"A simple calculator"<<endl;
cout <<"number:";
cin>>firstnumber;
cout<<"\n";
cout<<"\n(1)add (2)subtract (3)multiply (4)divide (5)modulo\n"
<< "\n(6)m+ (7)m- (8)mc (9)clear (10)exit\n\n"<<endl;
cin >> operand;
try
{
switch(operand)
{
case 1:
firstnumber=add(firstnumber);
break;
case 2:
firstnumber=substract(firstnumber);
break;
case 3:
firstnumber=multiply(firstnumber);
break;
case 4:
firstnumber=divide(firstnumber);
break;
case 5:
firstnumber=modulo(firstnumber);
break;
case 6:
memory+=firstnumber;
firstnumber=memory;
break;
case 7:
memory-=firstnumber;
firstnumber=memory;
break;
case 8:
firstnumber=memory;
memory=0;
break;
case 9:
firstnumber=0;
main();
return 0;
break;
case 10:
return 0;
}
}
catch(char *msg)
{
cout<<msg;
}
cout<<"\n\n the answer is:"<<firstnumber<<"\n\n";
system("PAUSE");
calculator(firstnumber);
return 0;
}
void calculator(double firstnumber)
{
int operand;
system("CLS");
cout<<memory<<endl;
cout<<"a simple calculator" << endl;
cout<<"number:"<<firstnumber<<"\n\n";
cout<<"\n(1)add (2)subtract (3)multiply (4)divide (5)modulo\n"<< "\n (6)m+ (7)m- (8)mc (9)clear (10)exit\n\n"<<endl;
cin>>operand;
try
{
switch(operand)
{
case 1:
firstnumber=add(firstnumber);
break;
case 2:
firstnumber=substract(firstnumber);
break;
case 3:
firstnumber=multiply(firstnumber);
break;
case 4:
firstnumber=divide(firstnumber);
break;
case 5:
firstnumber=modulo(firstnumber);
break;
case 6:
memory+=firstnumber;
firstnumber=memory;
break;
case 7:
memory-=firstnumber;
firstnumber=memory;
break;
case 8:
firstnumber=memory;
memory=0;
break;
case 9:
firstnumber=0;
main();
return;
break;
case 10:
return;
}
}
catch(int x)
{
cout<<"% not defined for modulo\n";
}
cout<<"\n\nthe answer is:"<<firstnumber<<"\n\n";
system("PAUSE");
calculator(firstnumber);
}