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Magazine Chapter 5: Problem 8
Suppose that the input is 38 45 71 4 -1. What is the output of the following code? Assume all variables are properly declared. cin >> num; sum = num; while (num != -1) { cin >> num; sum = sum + num; } cout << "Sum = " << sum << endl;
Short Answer
Expert verified
The output is "Sum = 158".
Step by step solution
01
Initial Input and Summation
The first number inputted is 38. This number is assigned to the variable `num`, and also to `sum`, so initially, both `num` and `sum` are 38.
02
Enter While Loop
Since `num` is not -1, the program enters the while loop. In the loop, the next number read from input is 45.
03
First Iteration in Loop
Inside the loop, `45` is added to `sum`, which was 38. Thus, the new `sum` is 38 + 45 = 83.
04
Second Iteration in Loop
The next number inputted is 71. This number is added to the current `sum` (which is 83), resulting in a new `sum` of 83 + 71 = 154.
05
Third Iteration in Loop
The following input number is 4. This value is added to the `sum`, which was 154, resulting in a new `sum` of 154 + 4 = 158.
06
Exit Loop Condition
The next input number is -1. Upon reading this number, the while loop exits because the condition `num != -1` fails.
07
Output the Sum
After exiting the loop, the program outputs the final value of `sum`, which is 158. The output displays "Sum = 158".
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Input Processing
In any C++ program, handling user input is crucial. Here, we start with the `cin` statement to capture the first numeric input from the user. This is stored in a variable called `num`. In our exercise, the initial value read is 38. In C++, `cin` continuously waits for user input during program execution and assigns the received value to the specified variable.
is a fundamental step as it determines how data from an external source is taken into the program for further processing. For a seamless experience, programmers should ensure the correct data type corresponds to the expected input. Mistakes in input handling can lead to errors or unintended behavior in the program.
is a fundamental step as it determines how data from an external source is taken into the program for further processing. For a seamless experience, programmers should ensure the correct data type corresponds to the expected input. Mistakes in input handling can lead to errors or unintended behavior in the program.
- Ensure correct data type alignment between input and storage variables.
- Understand that input is crucial for dynamic programming operations.
Loop Iteration
The `while` loop is a foundational construct in C++ for repetitive tasks. In this exercise, the loop repeatedly prompts for input and processes it as long as the condition holds true. Here, the condition is `num != -1`, which means the loop continues as long as the number input isn't -1.
Loop iteration starts with reading a new input and then updating the sum. After reading 38, the loop progresses, reading and adding further numbers: 45, 71, and 4. This looping pattern represents core programming logic, allowing a program to perform actions multiple times.
In each iteration:
Loop iteration starts with reading a new input and then updating the sum. After reading 38, the loop progresses, reading and adding further numbers: 45, 71, and 4. This looping pattern represents core programming logic, allowing a program to perform actions multiple times.
In each iteration:
- Inputs are newly read data values.
- The condition is checked.
- The body of the loop executes if the condition is true.
Accumulator Pattern
A common pattern in loops is the accumulator pattern, used here to sum numbers. This involves maintaining a cumulative total by adding new values to an ongoing sum. Initially, with the first input (38), `sum` is set to 38. With each pass through the loop, a new number adds to this total. After processing the numbers 45, 71, and 4, `sum` evolves to 83, 154, and finally 158.
The accumulator pattern is prevalent for any operation that needs to maintain a running total or count. It involves:
The accumulator pattern is prevalent for any operation that needs to maintain a running total or count. It involves:
- Initial setup of an accumulator variable (in this case, `sum`).
- Consistent updates as new data is processed.
- Final output of the accumulated result.
Conditional Statements
Conditional statements determine the flow of execution within a program based on specified conditions, using logic like `if`, `else`, and `while`. Here, our while loop's condition `num != -1` controls whether the loop continues. The loop exits once the condition becomes false.
This check is crucial because it ensures the program does not indefinitely request input. The use of `-1` as a marker to terminate the sequence is an example of a sentinel value, a special number not intended as normal data but as a signal to halt processing.
When programming:
This check is crucial because it ensures the program does not indefinitely request input. The use of `-1` as a marker to terminate the sequence is an example of a sentinel value, a special number not intended as normal data but as a signal to halt processing.
When programming:
- Understand which conditional checks govern loops and decisions.
- Use sentinel values cautiously to avoid confusion with genuine data inputs.
- Ensure conditions properly encapsulate the desired program logic.
