Section 4.3 Worked Example: If-Else Statements
Subgoals for Evaluating Selection Statements.
- Diagram which statements go together
- For if statement, determine whether expression is true or false
- If true – follow true branch, if false – follow else branch or do nothing if no else branch
Subsection 4.3.1
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Given the following declarations:
int alpha = 2, beta = 1, delta = 3, eta = 0, gamma = 0;
double omega = 2.5, theta = -1.3, kappa = 3.0, lambda = 0.0, rho = 0.0;
Evaluate these statements and determine the value of all variables used.
if (alpha > delta)
eta = alpha + 2;
else
gamma = alpha + 5;
Subsection 4.3.2 SG1: Diagram which statements go together.
If no { } are present, then by default all if and else branches have only a single statement:
if (alpha > delta)
eta = alpha +2;
else
gamma = alpha + 5;
Subsection 4.3.3 SG2: For if statement, determine whether true or false
First we evaluate (alpha > delta):
(2 > 3)
is FALSESubsection 4.3.4 SG3: If true, follow true branch. If false, follow else branch (OR do nothing if there is no else branch).
The condition is FALSE so we execute the else branch:
gamma = alpha + 5
= 2 + 5 = 7
Hint.
Answer: alpha = 2, beta = 1, delta = 3, eta = 0, gamma = 7
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