Section 11: Branching and Looping170
Conditionals and Conditional Branches
Often there are times when you want a program to make a decision. For example, suppose an accountant wishes to write a program that will calculate and display the amount of tax to be paid by a number of persons. For those with incomes of $10,000 per year or under, the amount of tax is 17.5%. For those with incomes of over $10,000, the tax is 22%. A flowchart for the program might look like this:
         
Start
         
                       
         
Prompt for
income amount
         
                       
         
Stop to key in
income amount
         
                       
     
Yes
Yes
Yes
Yes
Is
Income over
$10,000?
No
No
No
No
     
         
 
Compute
22% of income
         
Compute
17.5% of income
 
                         
                       
         
Display tax
         
                       
         
Stop
         
The conditional operations on your HP-41C are useful as program instructions to allow your calculator to make decisions like the ones shown above. The ten conditionals available in the HP-41C are shown below:
  X=Y?    tests to see if the value in the X-register is equal to the value in the Y-register.
  X=0?    tests to see if the value in the X-register is equal to zero.