structured programming

• subroutine

  a named ‘out of line’ block of code that may be executed (called) by simply writing its name in a program statement
• the two examples of subroutines

  • functions
  • procedures
• in general, a function interface includes:

  • identifier – the name of the function (this should be descriptive)
  • parameters – these are the function input (these must be passed in to the subroutine when it is called)
  • process – the ‘doing’ stuff
  • output – the return value
• advantages of structured programming

  • easier to understand and modify
  • modules (sections of code) can also be reused which reduces development time and it is
  • easier to independently test the individual modules
• local variables

  • variables created within a subroutine are called
  • these are only available for use in the function or procedure and once the subroutine ends, they are destroyed
• global variables

  • variables created outside of a procedure or function
  • it is best to avoid using these as they take up memory and increase the chance of naming clashes which could lead to bugs
• • if we want to get a value INTO a subroutine, we need to pass it in as a parameter
  • this is a value inside a bracket after the subroutine identifier
  • when we call the subroutine, we need to specify what these values are
• • if we want to get a local variable OUT OF a subroutine, we need to tell the function to RETURN that value
  • this is then stored as a variable in the program that called the function in the same way you would store a value from a user’s input
• • a function is a type of subroutine that returns a value
  • a procedure is a type of subroutine that does not return a value