3.6 Functions

• Modular programming and its importance
• Built-in and user-defined functions
• The syntax of a function: name, parameters, body, return value
• Parameter passing: formal and actual parameters, return values
• The scope of variables: local and global
• The role of functions in programming

• discuss the types of function used in modular programming
• use built-in and user-defined functions to create a modular program
• discuss the scope of variables and parameter passing between functions

“What are the roles of functions in programming?”

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1. Functions and modular programming
   40 min · 1 practice tasks · quiz
   What a function is, built-in versus user-defined, how to define and call one, and why breaking a program into functions is how all real software is built.
2. Parameter passing and variable scope
   40 min · 1 practice tasks · quiz
   How functions communicate through parameters and return values, and how local and global scope keep the parts of a program from interfering.
3. Why modular programming
   40 min · 1 practice tasks · quiz
   A kiosk till as one tangled script versus named functions - why real software is built in pieces.
4. Built-in functions in practice
   40 min · 1 practice tasks · quiz
   print, input, int, len, range, min, max, sum, type - ready-made tools, and why the language ships them.
5. Writing a function definition
   40 min · 1 practice tasks · quiz
   def, a meaningful name, colon, indented body - define greet once, then call it.
6. Parameters: giving a function data
   40 min · 1 practice tasks · quiz
   Zero, one or several parameters. Matched left to right. A VAT function that takes a price.
7. Return values: getting a result back
   40 min · 1 practice tasks · quiz
   return hands a value to the caller. print only shows a human. Catch the result in a variable.
8. Functions calling functions
   40 min · 1 practice tasks · quiz
   A final_bill that asks subtotal and add_vat to work - composition, and testing one piece at a time.
9. Formal and actual parameters
   40 min · 1 practice tasks · quiz
   length and width are formal; 5 and 3 are actual. The signature is the contract the caller must keep.
10. Local variables in practice
    40 min · 1 practice tasks · quiz
    Each call gets a fresh private total. When the function ends, the local name is gone.
11. Global variables and constants
    40 min · 1 practice tasks · quiz
    A name outside every function is global. Use it sparingly, mainly for true constants such as VAT 0.16.
12. Value-returning and void functions
    40 min · 1 practice tasks · quiz
    Some functions compute a result; some only do a job such as printing a receipt. Know which you are writing.
13. Building a modular program
    40 min · 1 practice tasks · quiz
    A school-mark reporter from small functions: input, average, grade, report - the 3.6 outcome in one sitting.
14. The roles of functions
    40 min · 1 practice tasks · quiz
    Reuse, simplicity, easier fixes, teamwork, readability - and abstraction as the idea underneath all five.