3.3 Identifiers and Operators

• The structural elements of a program: structure, syntax, errors
• Reserved words, identifiers and naming rules
• Data types
• Declaring variables and constants
• Input and output statements
• Operators: arithmetic, relational, logical and assignment
• Standard libraries

• describe the elementary elements of a computer program
• declare variables and constants in a programming language
• use input and output statements in a programming language
• use operators in a programming language
• appreciate the role of identifiers and operators in programming

“What is the importance of a structured programming language?”

“How are variables declared in programming languages?”

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1. The elements of a program: identifiers, variables and input/output
   40 min · 1 practice tasks · quiz
   The parts every program is made of, the rules for naming things, data types, declaring variables and constants, and reading input and displaying output.
2. Operators
   40 min · 1 practice tasks · quiz
   The four families of operator - arithmetic, relational, logical and assignment - how they work, precedence, and the store-versus-compare trap.
3. How a program is structured
   40 min · 1 practice tasks · quiz
   A program is ordered parts: comment, import, names, input, processing, output. Structure is why a language is usable.
4. Syntax and the three kinds of error
   40 min · 1 practice tasks · quiz
   Syntax is grammar. Syntax errors refuse to run; runtime errors crash; logic errors finish with the wrong change.
5. Reserved words you cannot use as names
   40 min · 1 practice tasks · quiz
   Keywords such as if, while, for and import belong to Python. They cannot be identifiers.
6. Identifiers and naming rules
   40 min · 1 practice tasks · quiz
   An identifier is a name you choose. Four rules, plus the unenforced rule: make it meaningful.
7. Data types: integer, float, string and Boolean
   40 min · 1 practice tasks · quiz
   A type is the kind of value. Whole shillings, decimal prices, names in quotes, and True or False.
8. Type conversion before arithmetic
   40 min · 1 practice tasks · quiz
   input() is text. int() and float() turn it into a number. str() turns a number into text. Forgetting this joins "50" and "20" into 5020.
9. Declaring variables in Python (and how C differs)
   40 min · 1 practice tasks · quiz
   A variable is a named box. Python creates it by assignment. C and Java state the type first. That is the inquiry question.
10. Constants: VAT, PI and a fee rate
    40 min · 1 practice tasks · quiz
    A constant is a named value that must not change. Python uses CAPITALS as a promise. Put VAT in one place.
11. Input statements: reading the user
    40 min · 1 practice tasks · quiz
    input() pauses, shows a prompt, and always returns a string. Convert, then store in a well-named variable.
12. Output statements: showing the result
    40 min · 1 practice tasks · quiz
    print() displays values. Several items can go in one print, separated by commas. Labels make the number mean something.
13. Arithmetic operators in Kenyan calculations
    40 min · 1 practice tasks · quiz
    Plus, minus, times, divide and modulus on real amounts: kiosk change, VAT, even and odd admission numbers.
14. Relational operators: questions that answer True or False
    40 min · 1 practice tasks · quiz
    == != < > <= >= ask questions. They produce Booleans, which every if will need in the next sub-strand.
15. Logical operators: and, or, not
    40 min · 1 practice tasks · quiz
    and needs both, or needs either, not reverses. That is how a real school or kiosk rule is written.
16. Assignment and compound assignment
    40 min · 1 practice tasks · quiz
    = stores right into left. += -= *= /= update a box in place. count += 1 is the standard step of a counter.
17. Operator precedence: when in doubt, brackets
    40 min · 1 practice tasks · quiz
    Times and divide before add and minus, as in mathematics. Brackets override and make the order readable.
18. Standard libraries: math and random
    40 min · 1 practice tasks · quiz
    import brings ready-made tools. math.sqrt and math.pi, random.randint. Reuse is professional, not cheating.