C# Numbers after decimal disappear after I join them with a string

Question

I have the following problem: After I add a string to my number the second digit after the point disappears like this

 var needed_product = sets * (2 * price_bananas) + 
                      sets * (4 * price_eggs) + 
                      sets * (0.2 * price_berries);

 var difference = Math.Abs(needed_product - amount_cash);

 if (amount_cash>=needed_product)
 {
    Console.Write("Ivancho has enough money - it would cost " + "{0:F2}", 
      needed_product + "lv."); 
 }

The output is 37,4 when it should be 37,40 with one more digit after the comma. How do I fix this problem? When I print it without adding the last piece of string the output of the integer is correct.

Answer 1

You are incorrectly formatting your string. Console.Write takes a string argument, and then optionaly some arguments afterwards to pass into the string.

In your example code, your string is

"Ivancho has enough money - it would cost " + "{0:F2}"

and then the argument you pass into that string is

needed_product + "lv."

needed_product is added to "lv.", and in the process being converted into a string without your custom parameters. This means that {0:F2} is converted into a string and ignores the F2 modifier, giving

"Ivancho has enough money - it would cost 37.4 lv."

Instead, use

Console.Write("Ivancho has enough money - it would cost {0:F2} lv.", needed_product); 

Answer 2

You could use a custom format within a toString() call.

   double value = 37.4;
   Console.WriteLine(value.ToString("0.00"));

Answer 3

The problem is that you are concatenating the decimal value with a string, before it's being formatted.

In other words, your current code is functionally equivalent to:

var temp = needed_product + "lv."; // this gets formatted using default formatting
Console.Write("Ivancho has enough money - it would cost {0:F2}", temp); 

To fix it, you should simply insert units into the actual format string:

Console.Write("Ivancho has enough money - it would cost {0:F2} lv", needed_product); 

Answer 4

If you run the following, fixed code:

void Main()
{
    var sets=6;
    var price_bananas=0.88;
    var price_eggs=1.10;
    var price_berries=0.37;
    var amount_cash=40;
    var needed_product = sets * (2 * price_bananas) + sets * (4 * price_eggs) + sets * (0.2 * price_berries);
    var difference = Math.Abs(needed_product - amount_cash);
    if (amount_cash >= needed_product)
    {
        Console.Write(
        "Ivancho has enough money - it would cost " 
        + "{0:F2} lv.", needed_product); 
    }
}

It produces the correct output:

Ivancho has enough money - it would cost 37,40 lv.

Explanation: The other way you were trying first converts the number to a string internally (by using the equivalent of the .ToString() method), and then later applies the formatting {0:F2} which became useless because the number is already a string, formatted by default options.

To avoid this, build up the complete formatting string, then add the parameters without modification (as shown in the code).