What is wrong with my C++ Code? I keep getting the wrong result

Question

I'm a beginner at programming and I'm trying to make a Kilometer and Miles converter application. I'm using codeblocks for my code. Choice 2 keeps giving me 0 as the result. Here's the exact code I'm typing:

#include <iostream>
using namespace std;
double choice, value1, result;
// I'm sure I messed up somewhere after this:
double value2 = .621371;
double value3 = 1.609344;
// Are these two lines ^ supposed to be here?
int main()
{
    while (true) {
        cout << "1. Kilometers to Miles" << endl;
        cout << "2. Miles to Kilometers" << endl;
        cout << "3. Exit the Application" << endl;
        cout << "Please enter a choice: ";
        cin >> choice;
        if (choice == 3)
            break;
        cout << "Please enter the first value: ";
        cin >> value1;
        // This if statement keeps giving me 0:
        if (choice == 2)
            result = value1 * value2;
        // I believe this part here is okay:
        else if (choice == 3)
            result = value1 / value3;
        cout << "The result is: " << result << endl;
    }
}

Answer 1

Here's how to fix your code:

1.Indent properly (Makes your code more readable)
2.This is making you code not work your code and is also very much unnecessary:
if(choice == 3) { break; }
3.Every single one of your if/else/else if statements need to have those curly braces after them:

if(whatever=whatever) {
     //whatever
}

4. Forget about using those break statements for programs this simple.
5. You missed "Kilometers to Miles".
6. The exit option is screwed up, change

else if(choice == 3)
result = value1 / value3  

to

else if(choice == 3) {
    return 0; // To end the program
}

7. Don't double the choice variable, it uses much, much, much, much more data then a simple intvalue (and what if the user enters 3.1 (or 4.838389, ect.) as a input?
8. You should make the precision of your result less, (you don't want 3.37374662232365 miles/kilometers, you want 3.3 miles/kilometers.) You can do that by also adding #include <iomanip> and adding in setprecision() before the declaring what "result" is (i.e: result = setprecision(1) value1 * value2;)
9. Including the whole std namespace is inappropriate in this case (it will slow your program down ALOT), so you should write std:: before each std function, or just write using std::whatever

Answer 2

I fixed the Problem Now. If any one can also comment below to me, is this a lot better than my original code? Basically is this new code a lot more readable to you all and is it more organized? I would love to get y'all's opinion on this updated code.

    #include <iostream>
float choice, value1, result;

int main(){
    while (true){
    std::cout << "Please enter a choice: " << std::endl <<
                 "1. Kilometers to Miles" << std::endl <<
                 "2. Miles to Kilometers" << std::endl <<
                 "3. Exit the Application" << std::endl;
    std::cin >> choice;
    if(choice == 3){
        break;
    }
    std::cout << "Enter the Value you would Like to Convert: ";
    std::cin >> value1;
    if (choice == 1){
        result = value1 * 0.62137;
    }
    else if (choice == 2){
        result = value1 * 1.609344;
    }
    std::cout << "The result is: " << result << std::endl;
    }
}