Question

Assume a string object has been defined as follows: string description; A) Write a cin statement that reads in a one-word string. B) Write a statement that reads in a string that can contain multiple words separated by blanks.

Short answer

Answer: To read a one-word string, use the cin statement as follows: ```cpp cin >> description; ``` For a multi-word string separated by blanks, use the cin.getline function like this: ```cpp cin.ignore(); // To clear any newline characters left in the input buffer getline(cin, description); ```

Step-by-step solution

Part A: Read a one-word string

To read a one-word string using a cin statement, simply use the following code: ```cpp cin >> description; ``` The operator will read the input until it encounters whitespace (such as a blank space or a newline).

Part B: Read a multi-word string separated by blanks

To read a string that contains multiple words separated by blanks, use the cin.getline function like this: ```cpp cin.ignore(); // To clear any newline characters left in the input buffer getline(cin, description); ``` The first line with cin.ignore() is used to clear any leftover newline characters in the input buffer, which could otherwise be treated as a new input. Then, the getline function is used to read the input till it encounters a newline. This allows the input to contain multiple words separated by blanks.

Key concepts

cin statement

In C++, the 'cin' statement is a fundamental tool for reading input from the standard input, which is usually the keyboard. It's a part of the iostream library and stands for 'character input'. When you write a line such as cin >> description;, it instructs the program to wait for the user to enter input, and upon pressing the Enter key, assigns that input to the variable 'description'.

However, cin uses whitespace (spaces, tabs, and newlines) to determine the end of an input value, which means it can only be utilized for reading single-word strings. As soon as cin encounters a space or any other whitespace character, it stops reading further input.

reading strings

Reading strings in C++ can be accomplished in various ways, but one common technique is to use the cin statement as described earlier. This approach works well for single-word inputs but falls short when you need to read a string of text that includes spaces. To address this limitation, C++ provides additional tools like the cin.getline function for more complex string inputs that can contain multiple words separated by spaces.

Understanding how to choose the right tool for reading strings in C++ is pivotal. For instance, a common mistake is trying to use cin >> description; for multi-word input, which will only capture the first word, leaving the rest unread in the input buffer.

cin.getline function

The cin.getline function is a powerful ally when you need to read an entire line of text, including spaces. The function signature is as follows:
istream& getline(istream& is, string& str, char delim = '');
In this case, getline(cin, description); will read characters from the input buffer until the newline character is encountered, which typically signifies the end of input when the user hits the Enter key.

Before using cin.getline, it's a good practice to clear the input buffer using cin.ignore(). This prevents any unexpected behaviors that may arise from leftover characters (such as a newline from a previous input) in the buffer.

input buffer in C++

The input buffer in C++ is an area where the input characters are temporarily stored before being used by the program. When a user types into the console and presses Enter, the typed characters sit in the input buffer until they are read by cin or another input function.

Understanding the state of the input buffer is crucial when dealing with input operations. If not managed properly, unwanted characters like newlines from previous inputs can create bugs or logical errors in the program. Clearing the input buffer appropriately, with functions like cin.ignore() ensures that your program reads fresh user input without interference from remnants of past inputs.