hey, im working on a program that uses a stack array to do a simple calculator. The only problem im having is with a bool function in one my STACK class, it should return true if the stack gets down to -1, and false if otherwise, but it ALWAYS returns true. it is accessed from the second if statement in main.

thank you for your help

#include<iostream.h>
#include<fstream.h>
#include"apstring.h"
#include"apvector.h"
#include"apstring.cpp"

class STACK
{
private:
int top;
double stack[20];
public:
STACK();
void push(double x);
double pop();
bool isEmpty()
{
if(top==-1){
return true;
}else{
return false;
}
}
double current ()
{
return stack[top+1];
}
};

class RPN: public STACK
{
public:
RPN();
void add();
void sub();
void mult();
void div();
};

//RPN Constructor
RPN::RPN()
{
}

void RPN::add()
{
double first=0, second=0, ans=0;
first = pop();
second= pop();
push(first + second);
ans=first+second;
cout<<"\nResult of addition: " <<ans<<endl<<endl;
}
void RPN::sub()
{
double first=0, second=0, ans=0;
first = pop();
second= pop();
push(first - second);
ans=first-second;
cout<<"\nResult of subtraction: " <<ans<<endl<<endl;
}
void RPN::mult()
{
double first=0, second=0, ans=0;
first = pop();
second= pop();
push(first * second);
ans=first*second;
cout<<"\nResult of multiplication: " <<ans<<endl<<endl;
}
void RPN::div()
{
double first=0, second=0, ans=0;
first = pop();
second= pop();
push(first / second);
ans=first/second;
cout<<"\nResult of division: " <<ans<<endl<<endl;
}

//Default Constructor
STACK::STACK()
{
top=-1;
for(int i=0;i<20;i++)
{
stack[i]=0;
}
}

//Constructor 1
void STACK::push (double x)
{
top++;
stack[top] = x;
}

//Constructor 2
double STACK::pop ()
{
double x = stack[top];
top--;
return x;
}


//Main
int main ()
{
int pushnum=0, pushcounter=1;
apstring choice;
apstring calcchoice;
STACK empty;
RPN b;
do{

cout<<"Enter 'push' or 'pop', and 'q' once you wish to make the calculations: ";
cin>>choice;

if(choice == "q")
{
break;
}

if(choice == "pop")
{
if(!empty.isEmpty())
{
b.pop();
cout<<"\nCurrent number is: "<<b.current()<<endl<<endl;
}else{
cout<<"\n\nPop limit reached!"<<endl<<endl;
}
}


if(choice == "push")
{

if(pushcounter<20)
{
cout<<"\n\nEnter number to push: ";
cin>>pushnum;
b.push(pushnum);
cout<<"\n\nCurrent number is: "<<pushnum<<endl<<endl;
}else{
cout<<"\n\nPush limit reached!"<<endl<<endl;
}
}

}while(choice != "q");

//----------------------------------------------------------------------
do{
cout<<"\n\nEnter 'add', 'sub', 'mult', 'div', or 'q' to quit: ";
cin>>calcchoice;
//Calculator Commands
if(calcchoice == "q")
{
break;
}
if(calcchoice == "add")
{
b.add();
}

if(calcchoice == "sub")
{
b.sub();
}

if(calcchoice == "mult")
{
b.mult();
}

if(calcchoice == "div")
{
b.div();
}
}while(choice != "q");
system("PAUSE");
return 1;
}

Your default constructor sets top to -1...therefore the condition is true. Is it sitting at -1 even after you've pushed some numbers?

yes, thats exactly the problem

thanks