Procedures

• A subroutine is a section of code that can be re-used several times in the same program
• A subroutine is separate from the main code
• A subroutine has to be called upon
• Subroutines are designed to be repeated
• What are the benefits of subroutines?

  They make programs easier to read - They reduce the duplication of code - In subroutines, complex problems are broken down into smaller chunks
• There are 2 types of subroutines - procedures and functions
• A procedure executes commands (e.g. printing something a certain number of times)
• A function produces information by recieving data from the main program and returning a value to the main program
• A function could take the radius of a sphere from the main program , calculate the sphere's area , and then return the value of the area to the main program
• A function requires parameters to work
• Parameters are the values that are to be transferred from the main program to the subroutine
• A procedure is a type of subroutine that runs independently of the main program
• A subroutine must be defined at the top of of the program before the main code , by typing def and the name of the subroutine

  
• The main program starts beneath the subroutine , against the left side of the editor

  
• In this code , the while true loop in the main program asks the user if they want to multiply , divide or stop the program - If they choose to multiply, the multiply subroutine is called , and this subroutine gets initiated and then returns to the main program once complete - If they choose to divide, the divide subroutine is called instead - Typing stop will break the loop

  
• Subroutines must be written first , with the rest of the program underneath

  
• Subroutines can be called in any order

  
• Programming languages use local variables and global variables
• A global variable can be used anywhere in the program
• A local variable can only be used in the subroutine it is created in
• This code uses global variables as it allows the program to ask the user to enter numbers in the main program