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Subgoals

Section 5.12 Worked Example: Nested If-Else Statements

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 no else branch

Subsection 5.12.1

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Given the following declarations:
int alpha = 2, delta = 3, eta = 0,

double omega = 2.5, kappa = 3.0;
Evaluate these statements and determine the value of all variables used.
if (omega > kappa)
{
    if (alpha < delta)
        eta = 5;
    else
        eta = 4;
}
else
   if (alpha > delta)
      eta = 3;
   else
      eta = 2;

Subsection 5.12.2 SG1: Diagram which statements go together.

In this diagram, the first thing to note is the parent/outer if-else statement highlighted in blue.
The true branch of the parent/outer statment contains an inner if-else.
Likewise, the else branch of the parent/outer statement contains an inner if-else.
Figure 5.12.1.

Subsection 5.12.3 SG2: For if statement, determine whether true or false

Because there are 2 sequential if-statements, we start with the first one, and then repeat SG2 and SG3 for the other.
First we evaluate (omega > kappa):
(2.5 > 3.0) is FALSE

Subsection 5.12.4 SG3: If true, follow true branch. If false, follow else branch (OR do nothing if there is no else branch).

The else branch contains another if-else statement, so we must repeat the SG2 and SG3.
Figure 5.12.2.

Subsection 5.12.5 SG2: For if statement, determine whether true or false

Start with the first if-statement in the inner sequence.
First we evaluate (alpha > delta):
(2 > 3) is FALSE

Subsection 5.12.6 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 follow the else branch.
eta = 2;
Answer.
omega = 2.5, kappa = 3.0, alpha = 2, delta = 3, eta = 2

Subsection 5.12.7 Practice Pages

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