Stack around the variable 'equation' was corrupted

I'm trying to make a calcula开发者_运维百科tor in VC++ and even though it runs, it keeps reading memory that I haven't told it to, and I don't know how to make it stop.

#include <iostream>
#include <ctype.h>

int main(){

char equation[4];
equation[3] = '\0'; //string terminator
int result;
bool wantsToContinue = true;
char yesOrNo;

equationPrompt:
std::cout << "Enter Equation: ";
std::cin >> equation;

while(wantsToContinue){

    switch(equation[1]){
    case '+':
        result = int(equation[0]) + int(equation[2]);
        break;
    case '-':
        result = int(equation[0]) - int(equation[2]);
        break;
    case '*':
        result = int(equation[0]) * int(equation[2]);
        break;
    case '/':
        result = int(equation[0]) / int(equation[2]);
        break;
    }

std::cout << std::endl << "Your answer is " << result << std::endl;
exitPrompt:
std::cout << "Exit? Y/N: ";
std::cin >> yesOrNo;

if(tolower(yesOrNo) == 'n'){
    wantsToContinue = true;
    goto equationPrompt;
}
else if (tolower(yesOrNo) == 'y')
    wantsToContinue = false;
else{
    std::cout << std::endl << "Unknown response." << std::endl;
    goto exitPrompt;
}
}
return 0;
}

---

You make it stop by not writing an arcane Frankenstein language mix of C and C++, but instead using real C++ string types:

#include <string>
#include <istream>
#include <iostream>


int main()
{
  std::string equation;
  std::cin >> equation;

  // now equation[0] is the first character
}

Note that int(equation[0]) is almost guaranteed not to be what you think. What you want is something like int x = std::atoi(equation[0]); or std::strtol(), but that only works for single digits. Probably much simpler to just stream into an integer, which performs an actual text-to-integer conversion:

int x, y;
std::string operand;

std::cin >> x >> operand >> y;

---

equation is an array of 4 chars.

std::cin >> equation;

reads an arbitrarily long string into that array. Type too much, and it will overflow, stepping on adjacent memory.

As @Kerrek SB says, you're better off using std::string, which doesn't have that problem.