Question

Write a do-while loop that asks the user to enter two numbers, The numbers should be added and the sum displayed. The user should be asked if he or she wishes to perform the operation again. If so, the loop should repeat; otherwise it should terminate.

Short answer

**Answer:** The purpose of `scanf(" %c", &answer);` is to read a single character input from the user, which determines if they want to perform the operation again. The space before `%c` in the format specifier is used to ignore any whitespace (like newline or space) that may be present before the actual character input. This ensures that the previously entered newline character after the numbers input doesn't get mistakenly read as the answer.

Step-by-step solution

Setup the loop structure

First, we need to create a do-while loop. The structure of a do-while loop is such that it starts with a "do" statement, followed by the code block that runs within the loop, and then ends with a "while" statement that contains the loop condition. ``` do { } while (/* loop condition */); ```

Prompt user for two numbers

Inside the do-while loop, we need to first prompt the user for two numbers and store them in variables. We can use scanf() to read the user inputs, but remember to initialize the variables first. For example: ``` int num1, num2; printf("Enter two numbers: "); scanf("%d %d", &num1, &num2); ```

Add the numbers, display the result

Now, we need to add the two numbers and display the result. We can use a separate variable to store the sum and then use printf() to display it. ``` int sum = num1 + num2; printf("The sum of %d and %d is %d.\n", num1, num2, sum); ```

Ask user if they want to perform the operation again

After displaying the result, we should ask the user if they want to perform the operation again. We can use a character variable to store the user's response and then check if it is 'Y' or 'y' (for yes). ``` char answer; printf("Do you want to perform the operation again? (Y/N): "); scanf(" %c", &answer); ```

Check the response and set loop condition

Finally, we need to set the loop condition in the "while" statement so that it checks if the user's response is 'Y' or 'y', indicating they want to keep running the loop. ``` } while (answer == 'Y' || answer == 'y'); ```

Complete Code

Here is the complete code for the exercise: ``` #include int main() { int num1, num2, sum; char answer; do { printf("Enter two numbers: "); scanf("%d %d", &num1, &num2); sum = num1 + num2; printf("The sum of %d and %d is %d.\n", num1, num2, sum); printf("Do you want to perform the operation again? (Y/N): "); scanf(" %c", &answer); } while (answer == 'Y' || answer == 'y'); return 0; } ```

Key concepts

Programming Loops

When learning C++, understanding the concept of programming loops is foundational as they allow you to execute a block of code repeatedly. This concept is particularly useful when you want to perform the same operation multiple times, as illustrated in the given exercise. The do-while loop is one of several loop types in C++. Unlike the for and while loops that check the condition before executing the code block, the do-while loop ensures that the code block is executed at least once before checking the condition. This unique feature is perfect when you expect the code block to be executed at least once, as in the case of processing user input.

Here's a simple breakdown of the do-while loop structure:

• do: This keyword begins the execution block.
• Code block: This is the sequence of statements that will run.
• while: Following the code block, this keyword is used with a condition in parentheses. If the condition is true, the loop will restart; if it's false, it will terminate.

In the exercise solution, the loop allows the user to keep adding numbers until they decide to stop. Without such loops, you would have to write redundant code to perform the same action multiple times.

User Input in C++

Gathering user input is one of the most interactive aspects of programming. In C++, input from the user is typically acquired using the scanf function or, in C++ specifically, stream objects like cin. For example, the code provided uses scanf to read integers from the console. The function waits for the user to enter values and then stores them in predefined variables. Properly initializing these variables before use is crucial to prevent undefined behavior.

Tips for Gathering User Input:

• Always prompt the user: Use clear prompts to indicate what input you're expecting from the user.
• Be clear on format: If specific formatting is required for the input, make sure to communicate that to avoid input errors.
• Handle incorrect inputs: Include error handling to manage instances where the user input doesn't meet expected parameters.

In the provided exercise, user input is used to gather two numbers and then determine whether to repeat the operation, showcasing a simple yet practical use of input functions in C++.

Condition Checking in C++

Condition checking serves as the decision-making cornerstone in programming. It allows a program to execute certain parts of the code when specific criteria are met. In C++, conditional expressions are evaluated to true or false and are often accompanied by relational and logical operators such as ==, && (logical AND), and || (logical OR).

In the context of our do-while loop example, the condition comes after the keyword while and determines whether the loop should continue running. In the exercise, the program checks if the user has entered 'Y' or 'y' after performing the addition of two numbers. It's essential for such conditions to be clear and correctly crafted to avoid infinite loops or premature termination of the program.

Elements of Effective Condition Checking:

• Use clear logical conditions: Ensure your conditions are straightforward and pertain to the logic of the program flow.
• Consider all possible outcomes: Account for every possible result of a condition to manage program control flow effectively.
• Keep it simple: Conditions should be as simple as possible to avoid confusion and potential errors.

In the completed exercise, the loop continues until the user inputs something other than 'Y' or 'y', which is the negation of the loop condition. This is a fundamental example of using condition checking to control the execution of program loops in C++.