Section 1.10 Worked Example: Operation Precedence
Subgoals for evaluating an assignment statement.
- Determine resultant data type of expression
- Update variable for pre operators based on side effect
- Solve arithmetic equation, operator precedence
- If = statement, is Left Hand Side (LHS) a variable? Check data type of copied value against data type of variable
- Update variable for post operators based on side effect
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Given the following code snippet, evaluate the final statement (the last line). If invalid, give the reason. If valid, what value is assigned to the variable? Note any possible side effects.
int alpha = 2, beta = 1, delta = 3, eta, gamma; double omega = 2.5, theta = -1.3, kappa = 3.0, lambda, rho; gamma = delta / (alpha + beta) % alpha;
Subsection 1.10.2 SG1 : Determine resultant data type of expression
The expression is the right-hand-side (RHS) of the statement:
delta / (alpha + beta) % alpha. At the beginning of the snippet, all of these variables were declared as
inttype, so all of the operations will also result in
If the expression had included any
doublevalues, the operations dealing with any
doublevalues would promote any
intvalue on the other side of the operator to a
doublevalue, and the result would be a
double, but that is not the case here.
Subsection 1.10.3 SG2: Update variable for pre-increment or pre-decrement operators (side effect)
NOT USED IN THIS EXAMPLE
Subsection 1.10.4 SG3: Evaluate arithmetic expression according to operator precedence
- The RHS may be easiest to conceptualize algebraically, by replacing the variables right away with their initialized values from the declarations above:
3 / (2 + 1) % 2.
- In the order of operations, parentheses have highest precedence, so we evaluate the addition within the parentheses first, resulting in a new expression: 3 / 3 % 2.
- Division and modulus have the same precedence, so we evaluate them left to right: 3 / 3 is 1, then 1 % 2 is 1. (Remember, the mod % operation returns the remainder after integer division.)
Subsection 1.10.5 SG4: If an assignment statement (=), is Left Hand Side (LHS) a variable? Check data type of value against data type of variable.
The LHS is a variable of type
int, and the RHS is type
int. This is valid.
Subsection 1.10.6 SG5: Update variable for post-increment or post-decrement operators (side effect)
NOT USED IN THIS EXAMPLE
Subsection 1.10.7 Questions to check understanding
Q1) Is the left-hand-side (LHS) of the statement a variable? What type?
Q2) What is the resulting type after evaluating the right-hand-side (RHS)?
Q3) Can the type of the RHS result be assigned to the LHS variable?
Q1-Answer) Yes, gamma is declared as an int
Q2-Answer) On the RHS, all of the values are int, so the result is also int
Q3-Answer) Yes, an int can be assigned to an int
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