Question 55

The attributes of the operators are:

• +: High precedence, Left-associative
• -: Medium precedence, Right-associative
• *: Low precedence, Left-associative

Expression to evaluate: $2 - 5 + 1 - 7 * 3$

Step 1: Evaluate the highest precedence operator +.

• The sub-expression is $5 + 1 = 6$.
• Substituting this gives: $2 - 6 - 7 * 3$.

Step 2: Evaluate the medium precedence operator -.

• The operator - is RIGHT-associative. Therefore, $2 - 6 - 7$ must be parenthesized from the right: $2 - (6 - 7)$.
• Evaluating inner subtraction: $6 - 7 = -1$.
• Evaluating outer subtraction: $2 - (-1) = 2 + 1 = 3$.
• Substituting this back into the expression yields: $3 * 3$.

Step 3: Evaluate the lowest precedence operator *.

• $3 * 3 = 9$.