Question

Consider the following code (and assume that it is embedded in a com- plete and correct program and then run): char next; int count = 0; cout << "Enter a line of input:\n"; cin.get(next); while (next != '\n') { if ((count%2) == 0) cout << next; count++; cin.get(next); } If the dialogue begins as follows, what will be the next line of output? Enter a line of input: abcdef gh

Short answer

Answer: The next line of output will be "aceh".

Step-by-step solution

Understand the code

The code starts by initializing a character variable 'next' and an integer variable 'count' with a value of 0. Then it prompts the user to enter a line of input. Once the user enters the input, the code reads the first character stored in the 'next' variable.

Traverse the input using the while loop

The while loop iterates through the input while the character 'next' is not a newline character ('\n'). Inside the loop, the code checks if the current value of 'count' is even, and if so, it prints the character stored in 'next'. After that, the value of count is incremented by 1, and the next character is read from the input.

Analyze the given input and predict the output

With the given input 'abcdef gh', the while loop will process one character at a time, and the output will be formed by every other character. Here is a breakdown of the output formation based on the input indexes: Index 0 (a): count = 0 -> even -> output: a Index 1 (b): count = 1 -> odd -> no output Index 2 (c): count = 2 -> even -> output: ac Index 3 (d): count = 3 -> odd -> no output Index 4 (e): count = 4 -> even -> output: ace Index 5 (f): count = 5 -> odd -> no output Index 6 (space): count = 6 -> even -> output: ace Index 7 (g): count = 7 -> odd -> no output Index 8 (h): count = 8 -> even -> output: aceh

Provide the answer

Based on the analysis, the next line of output after the given input would be: aceh.

Key concepts

C++ programming

C++ programming is a powerful high-level language that enables developers to write complex software ranging from operating systems to video games. As with any programming language, understanding its syntax and structure is key to success.

In our exercise, we see the creation of a simple C++ program that takes user input and processes it character by character. A fundamental concept illustrated in this example is variable initialization, where a 'char' type variable named 'next' and an 'int' type variable named 'count' are assigned starting values. The importance of initializing variables cannot be overstated, as it prevents undefined behaviors during the program's execution.

Another crucial aspect is the distinction between character literals and string literals. In C++, single quotes define a single character, while double quotes are used for strings. For instance, '' represents the newline character, which is pivotal for detecting the end of user input in our program.

Control structures

Control structures are fundamental elements that determine the flow of control in a program. C++ provides several control structures such as 'if', 'for', 'while', and 'switch', among others. These structures enable the programmer to make decisions, repeat operations, and alter the control flow based on certain conditions.

In the exercise provided, a 'while' loop is used in conjunction with an 'if' statement to create a simple but effective pattern. The 'while' loop continues to execute as long as the 'next' variable does not encounter the newline character. Within each iteration, the 'if' statement is used to decide whether to output the current character or not, based on the evenness of the 'count' variable. Understanding how these control structures interact is essential for C++ programmers, as it shapes the way a program responds to different inputs and behaves during execution.

Improvement advice for students includes focusing on the condition within the 'while' loop and the 'if' statement. Grasping how these conditions check for specific criteria helps to understand why only every second character from the user's input is outputted by the program.

Input/output operations

Input/output operations are crucial in C++ as they allow communication between the user and the program. The 'iostream' library in C++ provides 'cin' for input and 'cout' for output, which are used extensively.

In our example, 'cout' is used to prompt the user for a line of input, while 'cin.get(next)' is used to read a single character from the input stream. This granularity allows the program to process one character at a time. Understanding the difference between 'cin' and 'cin.get()' is significant. While 'cin' is typically used for formatted input like strings or numbers, 'cin.get()' reads raw data, character by character, including whitespaces and control characters.

Mastering input/output operations in C++ is foundational for implementing user interactions within a program. By analyzing the step-by-step solution provided, students can better understand the nuanced dance between reading input data and presenting output data, an interplay at the heart of many programs written in C++.