Question

Consider the following C++ code: string str1; string str2; char ch; int index; cin >> str1; cin >> str2; cin >> index; ch = str1[index]; str1[index] = str2[index]; str2[index] = ch; cout << str1 << " " << str2 << endl; Answer the following questions: a. What is the output if the input is Hello There 2? b. What is the output if the input is Diamond Gold 0? c. What is the output if the input is C++ Java 1?

Short answer

a: "Heelo Thlre" b: "Giamond Dold" c: "Ca+ J+va"

Step-by-step solution

Understand the Variables and Input

First, understand the role of each variable. `str1` and `str2` are strings that will hold the first two user inputs. `ch` is a character variable used for swapping characters between the two strings, while `index` is an integer determining the position of the character to swap. The program reads `str1`, `str2`, and `index` from the input.

Parse Input Example a

For part (a), the inputs are `Hello`, `There`, and `2`. These mean `str1` is "Hello", `str2` is "There", and `index` is `2`.

Swap Characters for Example a

Access the character at position `2` in both strings. `str1` has 'l' at index 2, and `str2` has 'e' at index 2. Swap these characters. After the swap, `str1` becomes "Heelo" and `str2` becomes "Thlre".

Output Result for Example a

After swapping, print `str1` and `str2`. The concatenated output is "Heelo Thlre".

Parse Input Example b

For part (b), the inputs are `Diamond`, `Gold`, and `0`. This sets `str1` to "Diamond", `str2` to "Gold", and `index` to `0`.

Swap Characters for Example b

The character at index `0` of `str1` is 'D', and for `str2` it is 'G'. Swap them. `str1` becomes "Giamond" and `str2` becomes "Dold".

Output Result for Example b

The resulting strings after the swap are printed as "Giamond Dold".

Parse Input Example c

In part (c), the inputs are `C++`, `Java`, and `1`. Hence, `str1` is "C++", `str2` is "Java", and `index` is `1`.

Swap Characters for Example c

At index `1`, the character from `str1` is '+', and from `str2` it is 'a'. Swap them. `str1` becomes "Ca+" and `str2` becomes "J+va".

Output Result for Example c

Finally, output the swapped strings, giving us "Ca+ J+va".

Key concepts

Character Swapping

In string manipulation, character swapping is a fundamental operation that allows us to switch characters between two positions, either in the same string or across different strings. In C++, you can achieve character swapping using a temporary variable. This simple mechanism ensures that neither of the original characters is lost during the swap. Here is a typical way of swapping two characters:

• The character at the specified index of the first string is stored temporarily.
• This character is then replaced by the character from the second string at the same index.
• The temporarily stored character is placed in the corresponding position in the second string.

For example, if `str1` is "apple" and `str2` is "grape" with an index position of 1, initially `str1` has 'p' and `str2` has 'r'. Post-swap, `str1` becomes "arple" and `str2` becomes "gpape".

Input Parsing

Input parsing refers to the process of reading and interpreting the data inputted into a program. In this context, C++ utilizes the `cin` function to capture user input. Consider the following:

• `str1` and `str2` are collected as strings using `cin >> str1 >> str2`.
• The `index` is captured as an integer that specifies which character positions will be swapped in the strings.

Let's break down Example (a) where the input is `Hello There 2`. We parse it into: - `str1` = "Hello" - `str2` = "There" - `index` = 2 Upon parsing, we gain the necessary information to perform operations on the specific char index within these strings.

Variable Roles

Every variable in a program serves a specific role and purpose. In the given C++ code:

• `str1` and `str2` are used to store the inputted strings.
• `ch` serves as a temporary storage used during the character swapping process.
• `index` indicates the exact character position in both strings where the swapping occurs.

Understanding these roles helps programmers predict the behavior of the code, particularly in multitasking environments. For instance, knowing that `ch` serves as a temporary storage for character swapping helps avoid incorrect overwriting of character values during the swap process.

Indexing in Strings

Indexing is a crucial concept in C++ string manipulation. Strings in C++ are arrays of characters, and each character has a specific index starting from zero.

• To access a character at a specific index, you can use the bracket `[]` operator.
• Remember, the first character of any string is at index 0, followed by index 1, and so on.

For example, in "Hello", the character at index 2 is 'l'. This ability to accurately index enables operations like comparison, insertion, and in this case, swapping specific characters easily. When dealing with large strings, efficient indexing plays a critical role in performance and correctness of operations such as character swapping.