C++ Programming - stack based calculator program

Can anyone see what I've done incorrectly with this program. You should be able to enter a value, press return, enter then next value, press return, enter an operator, press return and you'd get the answer, then you can just continue but would need to Ctrl+Z to exit.

[code]
#include <list>
#include <stack>
#include <string>
#include <iostream>

using namespace std;

void main (void)
{
cout << "enter value or operand" << endl;
stack <string> stk;
const int BUFLAN = 80;
char szbuf[BUFLEN+2] = {0};

for (;;)
{
string s;
cin >> s;
if (s== "+")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) + atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "-")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) - atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "*")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) * atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "/ ")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) / atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else
{
stk.push(s);
}
}
}
[/code/

Quote:

---

Originally posted by tinkerbelle
[/code/

---

can you fix that up?

Errors in your code:
=> Declared as BUFLAN and using as BUFLEN
=> Use sprintf, not sprint


Better use int main() and do a return 0 at the end, instead of void main

I corrected my typos, sorry, but now I'm getting a linking error LNK2001, _WinMain@16: Unresolved External Symbol. I looked it up, they say to go into the Output category of the Link field in the Project Setting dialog box, set the Entry Point symbol to wWinMainCRTStartup. I did this and it still gives me the same linking error....anybody seen this before?

C++ Programming - stack based calculator program
Can anyone see what I've done incorrectly with this program. You should be able to enter a value, press return, enter then next value, press return, enter an operator, press return and you'd get the answer, then you can just continue but would need to Ctrl+Z to exit.

Code:

---

#include <list>
#include <stack>
#include <string>
#include <iostream>

using namespace std;

void main (void)
{
cout << "enter value or operand" << endl;
stack <string> stk;
const int BUFLEN = 80;
char szbuf[BUFLEN+2] = {0};

for (;;)
{
string s;
cin >> s;
if (s== "+")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) + atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "-")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) - atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "*")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) * atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "/ ")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) / atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else
{
stk.push(s);
}
}
}

---

I got bored. If you want to wade through all of this fine. If not, so be it.
[code]
#include <list>
#include <stack>
#include <string>
#include <iostream>
//#include <cstdio> to get sprintf

using namespace std;

void main (void)
//use int main() instead of void main()
{
cout << "enter value or operand" << endl;
//place the cout line after declaring string s in for loop below
stack <string> stk;
const int BUFLEN = 80;
char szbuf[BUFLEN+2] = {0};

for (;;)
{
//all math operator you use are binary operator
//declare op1 and op2 here instead of in each operator
string s;
cin >> s;

//scrap everything below. It's not the syntax for a stack
//based calculator. See comments outside of code.
if (s== "+")
{
string op1 = stk.top();
//stk is still empty, nothing has been pushed on it yet
//therefore stk.top() is undefined
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) + atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "-")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) - atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "*")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) * atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else if (s== "/ ")
{
string op1 = stk.top();
stk.pop();
string op2 = stk.top();
stk.pop();
double result = atof(op1.c_str()) / atof(op2.c_str());
sprint (szbuf, "%f", result);
s=szbuf;
stk.push(s);
cout << "result: " << s << endl;
}
else
{
stk.push(s);
}
}
}
[/cout]


simple stack based operators usually have user push op1 on stack then push op2 on stack then enter operator. When operator is identified it goes back and pops op1 to become lhs operand and op2 to become rhs operand.

Code:

---

request op1
push op1 on stack
request op2
push op2 on stack
request operator
pop stack and store result as rhs
pop stack and store result as lhs
use switch based on char (not string) representing operator if you want, rather than if/else with string comparison.
switch(operator)
{
  case '+':
    result = lhs + rhs;
    break;
  case '-':
    result = lhs - rhs;
    break;
//etc.
}
display result.

---

for simple operations, probably not much advantage over non-stack based calculators. But trying to do this with a non-stack based calculator is very difficult. With a stack based calculator (and a few other tricks) it ain't a puff ball, but it ain't impossible either.

result = (5 * (4 - 1)/(7+ 8))*3;

post fix notation is the other trick to allow most efficient use of a stack based calculator to solve complex equations like above entered as a single string of input.

Good luck with your assignment.

Quote:

---

Originally posted by tinkerbelle
I corrected my typos, sorry, but now I'm getting a linking error LNK2001, _WinMain@16: Unresolved External Symbol.

---

You need to change the target from a Win32 GUI app to a Win32 console application.

Thanks, when I restarted the program, you know copy and pasted it back it. I was able to get rid of that error.

Now I still have a bug in the program, do I need to do something else with the / (divide) and the - (subtraction) operands because when I run it and use the / for division is just hangs, then when I use the - (for subtraction) it gives me a negative number...
i.e.

20
20
+
result: 40.000000

10
-
result: -30.000000

This is the first time I've run into this and then when I attempt to use the / (division) it just hangs. Suggestions please.

Your subtraction is subtracting the first number from the second number: 10 - 40 = -30, instead of the second number from the first number: 40 - 10 = 30.

Not sure about the problem with divide, but I think the operands are switched for that, too.

I think you should use a stack of numbers instead of a stack of strings.
That would be faster and it would make more sense, since the only thing you store on the stack is numbers.

I figured it out, of course, with all your help. Thanks much.