Introduction to Subroutines (AQA GCSE Computer Science)

What is a subroutine? 

• Subroutines are an out of line block of code that may be called by simply writing their name in a program     
• Subroutines are given a unique name so they can be called anywhere in a program
• There are many benefits to using subroutines, these include
  • Making bigger problems easier to break down (decompose) and code
  • Allows team members to be able to work on different parts of a problem
  • Makes the program easier to debug
  • Makes programs more efficient as code is not duplicated
• More detailed information about subroutines can be found in the 'Structured Programming' section

What are meaningful identifiers?

• Meaningful identifiers are sensible names used for variables, constants or subroutines
• A meaningful identifier must be used to help aid the maintainability of a program
• An example would be a variable used for an input of a users' first name

Meaningful Identifier	Poor Identifier
name ← USERINPUT IF name == "Mike" THEN cost ← 100 * 0.5 ELSE OUTPUT name + " your total is: " + cost	a ← USERINPUT IF a == "Mike" THEN b ← 100 * 0.5 ELSE OUTPUT a + " your total is: " + b

Examples of using subroutines

SUBROUTINE Information()     first_name ← USERINPUT     surname ← USERINPUT ENDSUBROUTINE

SUBROUTINE Tax(pay_per_hour, hours_worked)     total ← pay_per_hour * hours_worked     net_pay ← total * 0.8     RETURN net_pay ENDSUBROUTINE

//Main program starts here

Information()

OUTPUT(Tax)