C++ Troubleshooting my command line calculator - c++

Question

I am using xcode for my c++. It is a simple command line calculator.
This is what I have so far:
//
// main.cpp
// test
//
// Created by Henry Bernard Margulies on 8/21/13.
// Copyright (c) 2013 Henry Bernard Margulies. All rights reserved.
//
#include <iostream>
#include <string>
using namespace std;
int main()
{
bool loopy = true;
cout << "\nCalculator\n";
while (loopy == true)
{
bool gooy;
double answ; // answer
double fn; // first number
double sn; // second number
string opersym; // operation symbol
string oper; // operation
string more; // rerun the program or not
cout << endl << "Operation please (+, - , x or d): "; //Problem1
cin >> oper;
if (oper == "+") //makes sure operation is viable
{
gooy = true;
}
if (oper == "-")
{
gooy = true;
}
if (oper == "x")
{
gooy = true;
}
if (oper == "d")
{
gooy = true;
} //does the above
else
{
cout << endl << "Enter a real operation"; //complains if oper not viable
gooy = false;
continue;
}
if (gooy == true)
cout << endl << "First number please: ";
if(!(cin >> fn)) //makes sure it is a number
{
cerr << endl << "Enter a number next time, please try again"; //complaint
gooy = false;
loopy = true;
break; //Problem2
}
if (gooy == true)
{
cout << endl << "Next number: ";
if(!(cin >> sn))
{
cerr << endl << "Enter a number next time, please try again";
gooy = false;
loopy = true;
break; //Problem2
}
if (gooy == true)
{
opersym = oper;
if (oper == "+")
answ = fn + sn;
if (oper == "-")
answ = fn - sn;
if (oper == "x")
answ = fn * sn;
if (oper == "d")
{
opersym = "÷";
answ = fn / sn;
}
cout << endl << "You entered: " << fn << " " << opersym << " " << sn << ". And it equals " << answ;
cout << endl << "Want more? y/n: ";
cin >> more;
if (more == "n")
{
cout << endl << "Okay, I'm not wanted. Shutting down. :(";
return(0);
}
if (more == "y")
{
cout << endl << "Back to work!";
}
else
{
cout << endl << "Since you can not be bothered to type it right, I'll take it as a no. :(";
return(0);
}
}
}
}
return 0;
}
I have several requests:
First, only division seems to work. Check the first part of main where it asks for an operation and confirms it. It does not want to work for +, - or x, but only for d
2.Check the two comments named problem2. In these parts continue; and break; don't restart the calculator properly. I want to go back to the beginning of the while loop and goto is supposedly unstable and bad.
3.Could you correct my code? I am no expert and the whole thing is very dirtily done. Please show me better logic to make the code shorter, faster and more stable.
Thanks!
ps. I'm a 12 year old kid teaching myself c++ off the internet, so please cut me some slack and explain things like you're speaking to a puppy.

Answer 1

Your problem is the else after if (oper == "d") If the operation is not d, the else clause will activate, even if an operation was picked earlier. Try this instead.
if (oper == "+")
{
gooy = true;
}
else if (oper == "-")
{
gooy = true;
}
else if (oper == "x")
{
gooy = true;
}
else if (oper == "d")
{
gooy = true;
}
else
{
cout << endl << "Enter a real operation"; //complains if oper not viable
gooy = false;
continue;
}
Now the final else will only activate, if all previous else clauses were activated.
Alternatively
if (oper == "+" || oper == "-" || oper == "x" || oper == "d")
{
gooy = true;
}
else
{
cout << endl << "Enter a real operation"; //complains if oper not viable
gooy = false;
continue;
}
break exits the loop it is in. Try continue instead. It goes back to the top of the loop, and if the condition is true, starts over.
Try to declare variables closer to where they are used. For example answ and opersym are not used until late in the loop. You can declare them local to the if statement block for if (gooy == true)

Answer 2

first of all, good luck with learning C++. I am sure you'll pick it up in no time at all :) Here's a basic calculator. It's not ideal but shorter.
#include <iostream>
#include <string>
int main()
{
using namespace std; //use namespace only within the scope of main()
//ask user to choose operation
string operation = "";//good to initialize local variable. otherwise C++ assigns them garbage values
while(operation != "+" && operation != "-" && operation != "*" && operation != "/")
{
cout << "Please enter a mathematical operation. Options are: + or - or * or /" << endl;
cin >> operation;
}
cout << "You entered " << operation << endl << endl;
//ask user to enter two numbers
double number1 = 0, number2 = 0, result = 0;
bool success = false;//true if calculation carried out successfully
//keep looping till calculation carried out successfully
while(success!=true)
{
cout << "Please enter the first number: " << endl;
cin >> number1;
cout << "Please enter the second number: " << endl;
cin >> number2;
if(operation == "+") result = number1 + number2;
else if(operation == "-") result = number1 - number2;
else if(operation == "*") result = number1*number2;
else if(operation == "/" && number2 != 0) result = number1/number2;
else
{
cout << "Please enter non-zero value for number2 since carrying out division" << endl;
continue;
}
success = true;
cout << "Result is: " << number1 << " " << operation << " " << number2 << " = " << result << endl;
}
return(0);
}