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FAQ: Working with Numbers - Review

This community-built FAQ covers the “Review” exercise from the lesson “Working with Numbers”.

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Taking the example of calculating compound interest, how would you write something clean that would compound for X-amount of years? If it were able to calculate based on user input for X-years would be nice, but I can’t wrap my head around it at the moment. The code I have written so far is as follows:

double baseSavings = 2000.67;
Console.WriteLine (baseSavings);
double interestRate = 0.11;
Console.WriteLine (interestRate);
double firstYearInterest = (baseSavings * interestRate);
Console.WriteLine (firstYearInterest);
double firstYearTotal = (baseSavings + firstYearInterest);
Console.WriteLine (firstYearTotal);

I’ve written a basic spending tracker program as follows:

// List of monthly outgoings
decimal outBroadband = 25;
decimal outContactLenses = 25;
decimal outPetrol = 50;
decimal outMortgage = 538;
decimal outCouncilTax = 112;
decimal outUtilities = 55;
decimal outPhones = 10 + 10;
decimal outWater = 42;
decimal outInsurance = 54 + 10 + 16;
decimal outFood = 200;

  decimal outTotal = (outBroadband + outContactLenses + outPetrol + outMortgage + outCouncilTax + outUtilities + outPhones + outWater + outInsurance + outFood);
  decimal monthlyPay = 1621;
  decimal NDI = (monthlyPay - outTotal);
  // Calculations
  Console.WriteLine($"Monthly pay = £{monthlyPay}");
  Console.WriteLine($"Total outgoings = £{outTotal}");
  Console.WriteLine($"Net monthly disposal income = £{NDI}");

Is there a way to program so it automatically adds all of the ‘decimal outXs’ together without having to list each individual one (i.e. ‘decimal outTotal = (outBroadband + outContactLenses, etc.’).


Hi I am sort of stuck on this exercise.
I wrote a program that ask the user for there age and then tells the what age they are in dog years.

        int dogYears = 7;
        Console.Write("Please enter your age : ");
        int userAge = int.Parse(Console.ReadLine());

        Console.WriteLine("Your age in dog is " + userAge * dogYears);

I know my code works as I ran it in visual studio, but when I try runing it in Codecademy I get the fallowing errors.

Unhandled Exception: System.ArgumentNullException: Value cannot be null.
Parameter name: s
at System.Int32.Parse(String s)
at Review.Program.Main(String args) in /home/ccuser/workspace/csharp-working-with-numbers-review-working-with-numbers-csharp/Program.cs:line 21

can any one help?

Hi guys can some one look below and tell me why the netPay won’t show after (“My Pay Before tax is”

int netPay = 12500;
double vat = 0.20;

		double totalTax = netPay * vat;
  double grossPay = netPay - totalTax;
  Console.WriteLine("My Pay Before tax is", netPay);

Hello, @method5217209232. Welcome to the forum.

There are a couple of ways to include the value of your variable, netPay, in your output. I’m not sure which of these you may be more familiar with, but here are a few examples to consider:

string myString = "wild grapes";
Console.WriteLine("I like bananas, coconuts and " + myString + "!");
//or composite formatting:
Console.WriteLine("I like bananas, coconuts and {0}!", myString);


I like bananas, coconuts and wild grapes!
I like bananas, coconuts and wild grapes!

The {0} acts as a placeholder for the variable. If you wanted to include values from multiple variables, you just add more placeholders:

string item1 = "bananas";
string item2 = "coconuts";
string item3 = "wild grapes";
Console.WriteLine("I like {0}, {1} and {2}!", item1, item2, item3);


I like bananas, coconuts and wild grapes!

There is also string interpolation:

string item1 = "bananas";
string item2 = "coconuts";
string item3 = "wild grapes";
Console.WriteLine($"I like {item1}, {item2} and {item3}!");


I like bananas, coconuts and wild grapes!

Happy coding!