Question

Suppose that score is an int variable. Consider the following if statements: if (score > = 90) ; cout \(<<\) "Discount \(=108^{\mathrm{n}}<<\) endl a. What is the output if the value of score is \(95 ?\) Justify your answer. b. What is the output if the value of score is \(85 ?\) Justify your answer.

Short answer

The output is "Discount = 108" for both score = 95 and score = 85, due to the null statement after the if-condition.

Step-by-step solution

Examine the given statements

The given statement is an if-statement: if (score >= 90) ; cout << "Discount = 108" << endl; It is important to note the presence of a semicolon right after the if-condition: if (score >= 90) ;. This semicolon acts as a null statement, which means the actual block of code following the if-statement is independent and will always execute regardless of the condition.

Analyze for score = 95

Given score = 95, we check the condition (score >= 90). Since 95 is greater than or equal to 90, the condition is true. However, due to the semicolon right after the if-condition, nothing will occur in this branch. The output statement cout << "Discount = 108" << endl; will still execute regardless of the if-condition, because it is not dependent upon it. Therefore, the output will be "Discount = 108" followed by a new line.

Analyze for score = 85

Given score = 85, we check the condition (score >= 90). The condition is false since 85 is less than 90. Even though the condition is false, due to the semicolon that acts as a null statement - the if-statement does nothing. Thus, the output statement cout << "Discount = 108" << endl; will execute and the output will still be "Discount = 108" followed by a new line.

Conclusion

Regardless of the value of score (whether it is 95 or 85), the semicolon turns the if-statement into a no-operation, and the print statement executes in both cases, producing the same output.

Key concepts

Conditional Statements

Conditional statements are fundamental in C++ programming and many other programming languages. They allow developers to execute blocks of code based on whether a condition is true or false. When evaluating these statements:

• The `if` keyword is used to begin a conditional statement.
• An expression within parentheses ( ) follows the `if` keyword. This expression evaluates to either true or false.
• If the expression evaluates to true, the code block after the parentheses is executed.
• Else, the program will skip over the block of code intended for the `if` statement.

In our example, the condition is `(score >= 90)`. If `score` is 95, this condition is true, but due to a syntax issue, the output is misleading.

Syntax Error

Syntax errors occur when a programmer writes code that the compiler or interpreter does not understand. It is like a grammatical error in spoken language. In C++, syntax errors prevent the code from running correctly.

In the exercise, the presence of a semicolon after the if-condition `(if (score >= 90);)` creates an issue called a null statement, resulting in an unintentionally empty operation. When a semicolon immediately follows a condition, it signifies the end of that statement, effectively telling the program: "Do nothing if the condition is true."

Such mistakes commonly lead to bugs or unexpected behavior in programs. Recognizing syntax errors helps correct code logic, achieving desired outcomes.

Null Statement

A null statement in C++ is effectively a statement that does nothing. It is often represented by a standalone semicolon (`;`). While it can be used intentionally in certain situations, it sometimes appears due to mistakes in the code.

In the given exercise, the semicolon at the end of the if-condition `(if (score >= 90);)` makes the condition independent of the following code block. This means:

• If the condition `(score >= 90)` is true, no operation will occur because of the semicolon.
• Regardless of true or false, the line after the semicolon will execute.

Recognizing when semicolons cause null statements helps avoid situations where conditions do not control intended actions.

Output Analysis

Output analysis involves examining what a program will display when executed. It is important for understanding program behavior, especially when conditions and logic are involved.

With the exercise, the output analysis shows that regardless of whether `score` is 95 or 85, the result is the same - "Discount = 108." This constant output is due to the null statement, making the `cout` command always execute. The line `cout << "Discount = 108" << endl;` will display the text on the console each time.

Output analysis helps verify that programs behave as expected, and it can uncover logical issues within conditional structures.