Question

Write a program that uses a for statement to calculate and print the average of several integers. Assume the last value read is the sentinel 9999 A typical input sequence might be 10811799999 indicating that the program should calculate the average of all the values preceding 9999

Short answer

To calculate the average, sum the input integers until 9999 is encountered, count them, and divide the sum by the count.

Step-by-step solution

Initialize Variables

Start by defining variables needed for the calculation. Create a variable, `total`, to store the sum of the numbers, set to 0 initially. Also, create a variable `count` to keep track of how many numbers are entered, set to 0.

Create a For Loop to Read Input

Use a `for` loop to read input numbers. Within the loop, prompt the user to enter an integer each time the loop runs.

Check for Sentinel Value

Inside the loop, check if the entered integer is the sentinel value 9999. If it is, break out of the loop to stop taking inputs.

Accumulate Total and Count Values

If the input is not 9999, add the input value to `total` and increment `count` by 1. This ensures that all inputs except 9999 are summed and counted.

Calculate the Average

Once the loop ends, calculate the average by dividing `total` by `count` using `average = total / count`. Ensure that `count` is not zero before performing the division to avoid division by zero error.

Print the Result

Finally, print the calculated average to the console to display the result of the program.

Key concepts

For Loop

In C++ programming, a `for` loop is used to repeat a block of code a specific number of times. It's an efficient way to iterate over a fixed range of values. In the exercise, the `for` loop helps to read numbers from the user until a special condition is met - namely, reaching the sentinel value. The general structure includes three parts:

• Initialization: Initializes variables needed for the loop.
• Condition: Evaluates whether the loop should continue.
• Iteration: Updates the variables after each cycle.

This makes `for` loops perfect for cases where the exact number of iterations is determined from the start.

Sentinel Value

A sentinel value acts as a signal to end a loop. It's a special value that doesn't match any valid input, hence it stands out as the end point. In the given exercise, `9999` functions as the sentinel value. When the loop encounters this value, it stops processing further inputs. Using a sentinel value simplifies the logic needed to stop the loop without extra conditions. This practice ensures the program knows precisely when to halt processing and can focus on the entries that precede the sentinel.

Integer Arithmetic

Integer arithmetic is fundamental in programming for performing mathematical operations. It involves calculations like addition, subtraction, multiplication, and division on integer numbers. The exercise uses integer arithmetic to sum up all input numbers and then divide the total by the count to find the average. Remember that division involving integers can result in loss of precision. Here, because all numbers are integers, the average is calculated in a way that may truncate decimal points. Hence, if a high degree of accuracy is needed, it's useful to use data types that support floating-point arithmetic for the average calculation.

Input Validation

Input validation ensures that the user inputs data correctly before processing it. This is crucial in programming to prevent errors and unexpected behavior. In the exercise, validating inputs includes checking if the entered value is the sentinel, `9999`, which should trigger the end of input collection. A robust program should handle erroneous input gracefully, such as non-integer or erroneous values that can cause logic errors. Implementing checks inside the loop guards against these issues, ferries valid inputs through the subsequent processes smoothly, and enhances user experience.