如何修复 c++ 中的此计算器错误？

Question

I'm new to programming and I came across this problem im not sure why the output is negative can someone explain? Edit: Thanks for the help!

#include <iostream>
using namespace std;

int main()
{
  cout << "Enter your first number " << endl;
  int num1;
  cin >> num1;
  cout << "Enter your second number" << endl;
  int num2;
  cin >> num2;
  cout << "Would you like to add  a third number, if your answer is yes enter yes, if your 
  answer is no enter no" << endl;
  int yes;
  cin >> yes;
  yes = 1;
  int sum;
  if (yes == 1) {
    cout << "Enter another number" << endl;
    int num3;
    cin >> num3;
    sum = num1 + num2 + num3;
    cout << "Sum = " << sum << endl;

  } return 0;
             
     output: Enter another number
             Sum =-858993440

Answer 1

Your issue is coming from this check

  if (yes == 1) {

What you want to be checking for is a std::string instead. Since the inputted type is a string you need to take it as a string instead of a integer.

Something like this should work for you:

int main() {
int num1 = 0, num2 = 0, sum = 0;
std::string yes;
std::cout << "Enter your first number " << std::endl;
std::cin >> num1;
std::cout << "Enter your second number" << std::endl;
std::cin >> num2;
std::cout << "Would you like to add  a third number, if your answer is yes enter yes, if you answer is no enter no"
          << std::endl;
std::cin >> yes;

if (yes == "yes") {
    std::cout << "Enter another number" << std::endl;
    int num3 = 0;
    std::cin >> num3;
    sum += num3;
}
sum += num1 + num2;
std::cout << "Sum = " << sum << std::endl;
return 0;
}

Answer 2

From your program, I am guessing that you want to add multiple numbers together. The problem is, you are expecting a string and scanning an int. That is what I would term undefined behaviour, Not to mention if you are going to assign it a value explicitly just after scanning it. you probably do not even want to scan it.

This is how you expect a string and scan one:

std::string choice;

do {
    //whatever the hell you wanna do!
    std::cin >> choice;
} while (choice == "yes");

Answer 3

You input a data onto the variable yes in the wrong datatype.

So I think the standard I/O thread has crashed and cause you can not give a value to the variable num3 . And the num3 is not initialized. The memory maybe still has a uncertain value that makes this result.