3.3. Worked Example: Sequential If 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;

Evaluate these statements and determine the value of all variables used.

if (alpha > beta)
   eta = alpha + 2;
if (alpha > delta)
   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:

Sequential If Diagram of two separate if-statements

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 (alpha > beta):

(2 > 1) is TRUE

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

The condition is TRUE so we execute the true branch:

eta = alpha + 2

= 2 + 2

= 4

sequential if part 1

SG2: For if statement, determine whether true or false

Because there are 2 sequential if-statements, we need to repeat SG2 and SG3 for the second if-statement in the sequence.

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 and there is no else branch, so we do nothing.

sequential if part 2

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