simple while loop calculator - c++

Question

Hello im stuck at SUBTRACTION AND DIVITION AND I CANT FIGURE OUT WHAT CODE to use because when I try to subtract 10 i inputed it then it will loop since the while condition is not meet which it needs to be negative to terminate the loop and i inputed 2 for the second number then loop again then i putted -number which lead to terminate loop and subtract all the number but the result is -12 its always wrong in every number cant figure out why Please help
Also with divition, only my addition is working havent started the divition cuz i cant figure out how
#include <iostream>
using namespace std;
int amt2, total;
double subNumbers();
double amt=1;
double number=0;
int main() {
int chc=0;
int amt = 0;
int amt2 = 1;
cout << "Welcome again User!\n";
cout << "______________________________________________________________\n" << endl;
cout << "Mathematical Operations(Improved):\n\n";
cout << "\t[1]-Addition" << endl;
cout << "\t[2]-Subtraction" << endl;
cout << "\t[3]-Multiplication" << endl;
cout << "\t[4]-Division\n" << endl;
cout << "______________________________________________________________\n" << endl;
cout << "Type the number corresponding to your chosen operation: ";
cin >> chc;
```
switch (chc) {
case 1:
```
system ("cls");
cout << "\n\n\tOperation chosen: Addition";
cout << "\n______________________________________________________________" << endl;
cout << "\n\nInput positive numbers to use the operation and input a negative number to end the operation.\n\n";
cout << "Enter your number: ";`
cin >> number;
while (number >= 0) {
// add all positive numbers
amt += number;
// take input again if the number is positive
cout << "Enter another number: ";
cin >> number;
}
// display the sum
cout << "\nThe sum of all the numbers is: " << amt << endl;
break;
```
case 2:
system ("cls");
cout << "\n\n\tOperation chosen: Subtraction";
cout << "\n______________________________________________________________" << endl;
cout << "\n\nInput positive numbers to use the operation and input a negative number to end the operation.\n\n";
do{
cout << "Enter your number: ";
cin >> number;
amt=number-number ;
}while (number >= 0);// subtract all positive numbers
// display the difference
cout << "\nThe difference of all the numbers is: "<<amt;
return 0;
}}
```
enter code here

Answer 1

You are subtracting number from number:
amt = number - number; // Which is always 0
So that's why amt == 0 always.
So just change your loop to this:
while (true) {
cout << "Enter your number: ";
cin >> number;
if (number < 0) break;
if (amt == 0) amt = number;
else if (number >= 0) amt -= number;
}
What this does is that if amt == 0, then set amt to number. I have done this because as the default value of amt is 0 (due to int amt = 0;), when amt == 0, then we can assume that the user has entered the first number, and thus we can set amt to number. And then we can use -= operator, which basically means:
amt = amt - number;
But before all this, using if (number < 0) break; we can check if the user has entered a negative number, and if the user has entered a negative number, then the break keyword will break out of the while loop.