Chapter 5 Worked Solutions

Task 1 — Operator warmup

Arithmetic: NetAmount := PrincipalAmount + InterestAmount;
Comparison: if InstallmentAmount > 0 then
Logical: if (InstallmentAmount > 0) and (DueDate <> 0D) then

Task 2 — Formula extraction

GrossAmount := Quantity * UnitPrice;
DiscountAmount := GrossAmount * DiscountPct;
NetAmount := GrossAmount - DiscountAmount;

This is easier to test and review than one dense inline expression.

Task 3 — Precedence check

Without parentheses: A + B * C evaluates multiplication first.
With parentheses: (A + B) * C changes the business result.

Rule: always use explicit parentheses for money formulas.

Task 4 — Condition hardening

IsDue := DueDate <= Today;
HasAmount := Amount > 0;
HasValidStatus := not Paid;
if (IsDue and HasAmount) and HasValidStatus then
    Message('Ready for processing.');

Task 5 — Validation expression

if (Amount <= 0) or (DueDate = 0D) then
    Error('Installment must have a positive amount and a due date.');

Task 6 — Ready-to-post expression

Sample expression:

ReadyToPost := (Amount > 0) and (DueDate <> 0D) and (not Paid);

Why each condition exists:

Amount > 0: blocks non-postable financial rows.
DueDate <> 0D: blocks incomplete scheduling data.
not Paid: prevents duplicate posting.

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