Question

When does the following while loop terminate? \(\mathrm{ch}=^{\prime} \mathrm{D}^{\prime} ;\) \(\mathrm{while}\left(^{\prime} \mathrm{A}^{\prime}<\mathrm{ch} \& \& \mathrm{ch}<=\mathrm{z}^{\prime}\right)\) \(\mathrm{ch}=\operatorname{static}_{-} \mathrm{cast}<\mathrm{char}>\left(\mathrm{static}_{-} \mathrm{cast}<\mathrm{int}>(\mathrm{ch})+1\right)\)

Short answer

The loop terminates when `ch` exceeds 'z', which occurs when `ch` becomes '{'.

Step-by-step solution

Understanding the Loop Condition

The condition of the while loop is `('A' < ch && ch <= 'z')`. This means the loop continues as long as the character `ch` is greater than 'A' and less than or equal to 'z'. The character 'z' corresponds to the ASCII value 122.

Initial Value Evaluation

The loop begins with `ch = 'D'`. According to the ASCII table, 'D' has a value of 68. Check whether `('A' < 'D')` and `('D' <= 'z')` both hold true. Both conditions are true: 'D' is greater than 'A' (65) and less than or equal to 'z' (122). Thus, the loop will execute.

Inside the Loop - Character Increment

The statement inside the loop is `ch = static_cast(static_cast(ch) + 1)`. This converts the character `ch` to its integer ASCII value, adds 1 to it, and then casts it back to a character. Therefore, each iteration increases the ASCII value of `ch` by 1, effectively moving `ch` to the next character.

Iteration Process

Each iteration increases the ASCII value of `ch`: 'D'(68) to 'E'(69), 'E'(69) to 'F'(70), ..., 'Y'(89) to 'Z'(90). After each change, check the loop condition `('A' < ch && ch <= 'z')`. As long as these conditions remain true, iterations continue. The loop continues up to 'z' (122).

Identifying Loop Termination

When `ch` reaches 'z'(122), the next iteration makes `ch` become '{'(123), at which point the condition `('A' < '{')` is true, but `('{' <= 'z')` is false. Therefore, the loop terminates after the character value exceeds 'z'.

Key concepts

ASCII Characters

ASCII (American Standard Code for Information Interchange) is a character encoding standard that assigns each character a unique numerical code.
These codes represent letters, numbers, and symbols, linking them to specific integer values.
For instance, the uppercase letter 'A' corresponds to the numeric value 65, while 'z' is represented by 122.

• This uniformity allows computers to process textual data consistently across various platforms.
• ASCII includes both uppercase (e.g. 'A' to 'Z') and lowercase letters (e.g. 'a' to 'z'), along with digits and other symbols.

Understanding ASCII is crucial for tasks involving character comparison and manipulation, like the while loop in our exercise.

static_cast

In programming, a `static_cast` is a tool that helps convert a variable from one type to another, safely.
In our example, it is used to change the character `ch` into its corresponding integer ASCII value and back again into a character.

• This type of casting is primarily used in C++ for type conversion during compile time.
• It ensures that the conversion is safe and the program knows what to expect, avoiding unexpected behavior.

During the iteration, `static_cast(ch)` turns `ch` into an integer (its ASCII value), allowing arithmetic operations, such as incrementing, to be performed before converting it back to a character using `static_cast`.

Loop Termination

Loop termination occurs when a loop's condition is no longer satisfied.
In our exercise, the loop condition is `('A' < ch && ch <= 'z')`, meaning it continues as long as `ch` is greater than 'A' and less than or equal to 'z'.

• The loop starts with `ch` as 'D' (ASCII 68), incrementing each time through the character sequence.
• It continues until `ch` surpasses 'z' (ASCII 122), becoming '{' (ASCII 123).
• At this point, `ch <= 'z'` is false, thus ending the loop.

Understanding when and how loops terminate is key to controlling program flow and avoiding infinite loops.

Character Increment

Character increment involves increasing the ASCII value of a character by adding to its integer form.
This operation effectively shifts the character to the next one in the ASCII sequence.

• In the provided exercise, this is performed by the line `ch = static_cast(static_cast(ch) + 1)`.
• This command takes the current character, converts it to its ASCII value, adds one, and converts it back.

Each increment moves `ch` up one character, like from 'D' (68) to 'E' (69). This step-by-step character change is essential in loops that require systematic iteration through a set range of characters.