Exercise - Build a calculator program

Completed

In this exercise, continue working on the calculator program that you created in the first exercise. Take all that hard-earned knowledge and implement the remaining functionality like user input and apply an arithmetic operator.

Read from the console

In this part, you add support for reading from the console.

1. Go to the directory Variables, and open the Program.fs file.

2. Locate the following code:

   printfn "Welcome to the calculator program"
   // read input from the console and assign to `sum`
   let sum = 0
   printfn "The sum is %i" sum
   

3. Replace the commented line with the following code:

   printfn "Type the first number"
   let firstNo = System.Console.ReadLine()
   printfn "Type the second number"
   let secondNo = System.Console.ReadLine()
   printfn "First %s, Second %s" firstNo secondNo
   

   Save the file and run the program next.

4. Run the command dotnet run.

   dotnet run
   

5. Fill in 1 and 2 when asked for input.

   Your output looks similar to:

   Welcome to the calculator program
   Type the first number
   1
   Type the second number
   2
   First 1, Second 2
   The sum is 0
   

   At this point, you're supporting user input, but you need the program to actually calculate, so let's do that next.

Perform a calculation

To add the calculation part of the program, convert the user input to numbers and apply an arithmetic operator.

1. Locate the row that looks like so:

   let sum = 0
   

   Change it to the following code:

   let sum = (int firstNo) + (int secondNo)
   

   Save your changes and rerun the program.

2. Run the command dotnet run.

   dotnet run
   

3. Enter 1 and 2 when asked for input.

   You see output similar to:

   Welcome to the calculator program
   Type the first number
   1
   Type the second number
   2
   First 1, Second 2
   The sum is 3
   

Congratulations! Your calculator program works as it should.