Question

If the sub-expression on the left of the ______ logical operator is false, the right sub-expression is not checked.

Short answer

Answer: The AND logical operator (&&) does not check the right sub-expression when the left sub-expression is false. This property, known as the short-circuit property, helps optimize program execution by avoiding unnecessary calculations.

Step-by-step solution

Identify the AND logical operator

The AND logical operator is denoted by "&&." It is used to compare two expressions. The result will be true if and only if both expressions are true.

Understand the short-circuit property of the AND operator

The short-circuit property is a feature of the AND operator. When the left sub-expression of the AND operator is false, there is no need to evaluate the right sub-expression, as the operator will be false regardless of the right sub-expression's value. This helps in optimizing the program's execution by avoiding unnecessary calculations.

Fill in the blank

Based on the analysis and understanding of the AND operator with its short-circuit property, we can now fill in the blank in the given statement. The correct statement would be: "If the sub-expression on the left of the `&&` logical operator is false, the right sub-expression is not checked."

Key concepts

Short-Circuit Evaluation

Short-circuit evaluation is a programming technique used to increase efficiency by 'skipping' the evaluation of logic when the final outcome is already certain. This concept is especially useful in the context of logical operators, such as AND (&&) and OR (||), in C++. For instance, when using the AND operator, if the first expression evaluates to false, there's no need to check the second one because the overall condition can never be true regardless of the result of the subsequent condition.

Let's take a practical example. Imagine checking if a user is logged in and has admin privileges. In code, this might look like if (isLoggedIn && isAdmin). Now, if isLoggedIn is false, the program skips the evaluation of isAdmin because, for the user to have admin privileges, they must be logged in first. This not only speeds up the program by avoiding unnecessary checks but also can prevent potential errors from occurring if, for example, isAdmin makes no sense to evaluate when isLoggedIn is false.

Logical Operators in C++

In C++, logical operators are used to form complex conditional expressions and include AND (&&), OR (||), and NOT (!). These operators are fundamental in control structures like if-else statements and loops, allowing developers to combine multiple conditions.

The AND operator, represented by &&, will return true if both operands are true. Contrastingly, the OR operator, symbolized by ||, returns true if at least one operand is true. The NOT operator, denoted by !, simply inverts the truth value of its operand. Understanding these operators is important for creating efficient conditions within your code.

• && evaluates to true if both conditions are true.
• || evaluates to true if at least one condition is true.
• ! inverts the true/false value of a condition.

Using logical operators correctly can significantly impact the readability and functionality of a program.

Conditional Expression Optimization

Conditional expression optimization is the process of refining logical expressions for efficiency and clarity. By carefully organizing and sometimes simplifying conditions, programmers can make the code not only run faster but also become more readable.

For example, in expressions involving an AND operator, placing the condition with the highest chance of being false first can make the expression run faster due to short-circuit evaluation. If you're testing multiple conditions, it's wise to order them from the most to the least likely to be true (for an OR operator) or false (for an AND operator).

Best Practices for Optimization

A few best practices include avoiding unnecessary calculations, using short-circuit evaluation to your advantage, and eliminating redundant conditions. By paying attention to these details, not only do you optimize performance, but you can also prevent bugs that might arise from evaluating unnecessary conditions which might not be valid under certain circumstances.