Question

Suppose that score is an int variable. Consider the following if statements: i. if (score = \(=70\) ) cout \(<<\) "Grade is \(\mathrm{C}\). " \(<<\) endl ii. if (score \(=70\) ) cout \(<<\) "Grade is \(\mathrm{C}\). \(^{\prime \prime}<<\) endl Answer the following questions: a. What is the output in (i) and (ii) if the value of score is \(70 ?\) What is the value of score after the if statement executes? b. What is the output in (i) and (ii) if the value of score is \(80 ?\) What is the value of score after the if statement executes?

Short answer

In (i), outputs "Grade is C." if score is 70; score remains unchanged. In (ii), always outputs "Grade is C." because score is assigned to 70.

Step-by-step solution

Understanding the First if Statement

The first statement is `if (score == 70) cout << "Grade is C." << endl;`. This is a comparison statement that checks if `score` is equal to 70. If `score` is 70, it will print "Grade is C." Otherwise, it will do nothing. Importantly, this does not change the value of `score`.

Analyzing the First if Statement with score = 70

When `score` is initially 70, the condition `(score == 70)` in the first statement evaluates to true. Therefore, it prints "Grade is C." The value of `score` remains 70 after execution.

Analyzing the First if Statement with score = 80

If `score` is 80, the condition `(score == 70)` is false, so nothing is printed and the value of `score` remains 80.

Understanding the Second if Statement

The second statement reads `if (score = 70) cout << "Grade is C." << endl;`. Here, `score = 70` is an assignment, not a comparison. This will set `score` to 70 and then always evaluates to true because any non-zero value in a condition is treated as true in C++.

Analyzing the Second if Statement with any initial score

Regardless of the initial value of `score`, the statement `score = 70` makes `score` 70 and then results in true. Therefore, it prints "Grade is C." and leaves `score` as 70.

Key concepts

Comparison operators

Comparison operators are vital in C++ programming as they help evaluate conditions within your code. They compare two values or expressions and return a Boolean result, which can either be true or false. This enables programmers to make decisions based on data.
The most common comparison operators include:

• `==`: Checks if two values are equal.
• `!=`: Checks if two values are not equal.
• `>`: Checks if the left value is greater than the right.
• `<`: Checks if the left value is less than the right.
• `>=`: Checks if the left value is greater than or equal to the right.
• `<=`: Checks if the left value is less than or equal to the right.

In the original exercise, `==` is used to verify if `score` equals 70. This comparison is fundamental in programming for control flow and decision-making processes.

Assignment operators

Assignment operators perform the task of assigning values to variables. The most common assignment operator in C++ is `=`. It assigns the right-hand value to the left-hand variable.
However, confusion often arises, as seen in the original exercise, due to its similarity to the comparison operator `==`.
### Common Assignment Operators

• `=`: Assigns the right-hand value to the left variable.
• `+=`: Adds the right value to the left variable and assigns the result to the left variable.
• `-=`: Subtracts the right value from the left variable and assigns the result to the left variable.
• `*=`: Multiplies the right value with the left variable and assigns the result to the left variable.
• `/=`: Divides the left variable by the right value and assigns the result to the left variable.

In the second if statement of the exercise, `score = 70` assigns the value 70 to `score`, demonstrating an assignment operation rather than a comparison.

C++ programming basics

C++ is a foundational programming language known for its efficiency and powerful features. Understanding C++ basics lays the groundwork for solving complex problems and developing sophisticated software.

Key C++ programming concepts include:

• **Data Types and Variables**: Integral to C++ are its data types (such as `int`, `float`, `double`, `char`) and variables, which store and manipulate data.
• **Control Structures**: Includes `if`, `else`, `for`, `while` loops, which control the flow of the program.
• **Functions**: Used for creating reusable code blocks, promoting modularity in programming.
• **Syntax**: A strict set of rules that specify the combinations of symbols that are considered to be correctly structured programs.

C++ also distinguishes between statements that produce a side effect (like assignments) and those that evaluate conditions (like comparisons), critical concepts as seen in the exercise's `if` statements.

Debugging logical errors

Logical errors in programming can cause unintended behavior or incorrect results. They can be tricky to identify since the program runs but does not produce the expected output.
### Tips to Debug Logical Errors:

• **Trace Your Code**: Manually walk through your code line by line to understand its flow and identify the issue.
• **Utilize Print Statements**: Insert print statements to check the state of your variables at different stages.
• **Use Debugging Tools**: Many IDEs offer built-in debuggers that allow you to step through your code and inspect variables.
• **Review Logic**: Double-check conditional statements and loops to ensure they perform as intended.
• **Compare Against Expected Behavior**: Ensure your program's output matches the expected results.

In the exercise, mistaking `=` for comparison rather than assignment results in a logical error. Recognizing and fixing these errors is crucial for developing reliable software.