如果语句在C＃中不起作用

Question

I'm using a tutorial to write a simple app that calculates how many years it will take for a bank account to reach a target amount.

I'm trying to use an "If" statement, so if the person's beginning balance is more than their target amount, it prints "Your balance is bigger than the target amount", but when I write this into my code, it always prints the above no matter what amounts the user inputs.

Here's the code:

        double balance, interestRate, targetBalance; //creating three doubles

        Console.WriteLine("What is your current balance?"); //writing to the console
        balance = Convert.ToDouble(Console.ReadLine()); //reading what the user inputs & converting it to a double

        Console.WriteLine("What is your current annual interest (in %)?");
        interestRate = 1 + Convert.ToDouble(Console.ReadLine()); //same as above

        Console.WriteLine("What balanec would you like to have?");
        targetBalance = Convert.ToDouble(Console.ReadLine()); //same as above

        int totalYears = 0; //creates an int variable for the total years

        do
        {
            balance *= interestRate; //multiplying balance x interest rate
            ++totalYears; // adding 1 to the total years
        }
        while (balance < targetBalance); //only do the above when balance is less than target balance


        if (balance < targetBalance)
        {
            Console.WriteLine("In {0} year{1} you'll have a balance of {2}.", totalYears, totalYears == 1 ? "" : "s", balance); //writing the results to the console
        }
        else if (targetBalance < balance)
        {
            Console.WriteLine("Your balance is bigger than the target amount");
        }
        Console.ReadKey(); //leaving the results there until the user inputs a key

Answer 1

The only way for your do-while loop to exit is when the balance is >= the target balance. Because of this, your first if statement will never evaluate to true .

You probably want to do your targetBalance < balance check before you enter your do-while loop. If the balance is greater than the target, start over. And then after the loop, there is no need to do the if check around your 'In x years...' dialog.

Answer 2

It works fine here. But please check your balance,targetBalance first. You didn't notice that what would happen If they are equal.

Answer 3

I think you want this...

double balance, interestRate, targetBalance; //creating three doubles

Console.WriteLine("What is your current balance?"); //writing to the console
balance = Convert.ToDouble(Console.ReadLine()); //reading what the user inputs & converting it to a double

Console.WriteLine("What is your current annual interest (in %)?");
interestRate = 1 + Convert.ToDouble(Console.ReadLine()); //same as above

Console.WriteLine("What balanec would you like to have?");
targetBalance = Convert.ToDouble(Console.ReadLine()); //same as above

int totalYears = 0; //creates an int variable for the total years
if (balance < targetBalance)
{
    do
    {
        balance *= interestRate; //multiplying balance x interest rate
        ++totalYears; // adding 1 to the total years
    }
    while (balance < targetBalance); //only do the above when balance is less than target balance
        Console.WriteLine("In {0} year{1} you'll have a balance of {2}.", totalYears, totalYears == 1 ? "" : "s", balance); //writing the results to the console
    }
 }
 else if (targetBalance < balance)
 {
     Console.WriteLine("Your balance is bigger than the target amount");
 }
 Console.ReadKey(); //leaving the results there until the user inputs a key