3.2. Worked Example: If-Else StatementsΒΆ

Subgoals for Evaluating Selection Statements

  1. Diagram which statements go together.

  2. For if-statement, determine whether expression is true or false.

  3. If true, follow true branch. If false, follow else branch (OR do nothing if there is no else branch).

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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;

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;

SG2: For if statement, determine whether true or false

First we evaluate (alpha > delta):

(2 > 3) is FALSE

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

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