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Chapter 6 - IF Statements
Structured Programming uses 3 Basic Control Structures:
1. Sequence - actions executed in the order that they appear
2. IF-THEN-ELSE - choice between two alternatives (or CASE for more alternatives)
3.DO-LOOP or repetition (FOR) - repeated execution of a loop
No GOTOs!!!!!
IF condition THEN
Clause
ELSE
Clause
END IF
Single Line IFs need no END IF
IF condition THEN statement ELSE statement
Comparing strings – based on numerical and alphabetical order, case sensitive:
number < uppercase < lowercase
ALU returns –1 if true, 0 if false
Nested IFs:
SELECT CASE test expression
CASE IS match expression
Statement(s)
CASE IS match expression
Statement(s)
CASE IS match expression
Statement(s)\
CASE ELSE
Statement(s)
END SELECT
Accumulators:
Counters: count number of times something happens
incremented by one each event (action or pass through loop)
Running Total: used to sum the values a variable is assigned
Logical Operators: (truth table page 182)
- NOT
- AND both must be true
- OR either one or both true
- XOR one, but not other true
- EQV both true or both false
- IMP (implication)
Order of precedence:
Parenthesis, Arithmetic operators, relational (< , = , >), NOT, AND, OR or XOR, EQV, IMP
Data Validation: (example: SS# is nine digits)
- reasonableness check age is positive
- range check input is within valid range
- value or code check input is a valid value
- digit check serial numbers begin with specific digit
When errors are detected, use the BEEP statement to alert the user
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