Question

Suppose num1 and num2 are int variables and symbol is a char variable. Consider the following input: 47 18 * 28 $ What value (if any) is assigned to num1, num2, and symbol after each of the following statements executes? (Use the same input for each statement.) a. cin >> num1 >> symbol >> num2; b. cin >> symbol >> num1 >> num2; c. cin >> num1; cin.get (symbol); cin >> num2; d. cin >> num1 >> num2; cin.get (symbol); e. cin.get (symbol); cin >> num1 >> num2;

Short answer

a) num1=47, symbol=18, num2=28; b) symbol=47, num1=18, num2=28; c) num1=47, symbol=' ', num2=18; d) num1=47, num2=18, symbol=' '; e) symbol=' ', num1=47, num2=18.

Step-by-step solution

Analyze Input and Statement (a)

Given the input "47 18 * 28 $" and the statement 'cin >> num1 >> symbol >> num2;', the extraction process reads 47 into num1, 18 into symbol (as it is the first non-digits after 47), and * into num2 after adjusting based on input interpretation, this recognition must be adjusted to match the scenario provided and normally store 18 into symbol * , skipping whitespace and store 28 into num2.

Analyze Statement (b)

For the statement 'cin >> symbol >> num1 >> num2;', the input "47 18 * 28 $" is processed where 47 is assigned to symbol, 18 to num1, and 28 to num2. The * is skipped in the process since after reading 47, the first character assumed as integer will be incorrectly processed.

Analyze Statement (c)

Using 'cin >> num1;' followed by 'cin.get(symbol);' and then 'cin >> num2;', the input "47 18 * 28 $" assigns 47 to num1. The cin.get() function captures the character space after 47, which is a whitespace, to symbol. The num2 is then read as 18 after skipping space.

Analyze Statement (d)

With 'cin >> num1 >> num2;' followed by 'cin.get(symbol);', the input "47 18 * 28 $" assigns 47 to num1 and 18 to num2. The cin.get() captures the whitespace character after 18, which will actually avoid any skipping and capturing of the * character.

Analyze Statement (e)

The statement 'cin.get(symbol);' followed by 'cin >> num1 >> num2;' on the input "47 18 * 28 $" results in the first capture of whitespace character into symbol from start assuming first character or whitespace different than 47. Then, 47 stores into num1 and 18 into num2, due to skipping first by whitespace reading.

Key concepts

cin stream

The `cin` stream in C++ is a crucial feature for obtaining user input. It stands for console input, and it's used to read data from standard input, typically the keyboard. The goal is to sequentially extract input data from the user and store it into corresponding variables. For example, with the expression `cin >> num1 >> num2;`, the input is read from the standard input buffer and stored sequentially in the variables num1 and num2.

The `cin` stream is designed to automatically skip whitespace, such as spaces, tabs, and newlines during extraction. This simplifies user input by allowing the user to separate input values with spaces or newlines without affecting the parsing process. However, this automatic whitespace skipping can also trip up new programmers if they are not expecting it or when reading character data. Thus, understanding how `cin` handles different types of input is essential when expecting data in various formats.

variable assignments

In C++, variable assignments are used to store values in variables that can later be used in calculations or logical operations. When using `cin` to assign values, the variables are updated in the order that inputs are extracted from the stream.

For example, if you have `cin >> num1 >> symbol >> num2;` and the input is "47 18 * 28 $", the first number (47) is assigned to num1. The stream then attempts to interpret the next input as a character for symbol, which after careful understanding, captures the non-digit input - the '*', and finally assigns the next integer (18) to num2 after interpreting spaces appropriately based on understanding and variable types. Thus, the order of assignments in variables should reflect the expected order of the inputs.

character handling

Character handling becomes significant when dealing with a mixture of numbers and characters in input. The C++ `cin` stream can seamlessly read characters placed in between numeric inputs, but its automatic whitespace skipping feature can cause characters like spaces or tabs to be accidentally ignored or misread.

To handle this, the `cin.get()` function is used. This function reads the next single character in the input stream, including whitespace. Understanding `cin.get()` is essential for reading characters and spaces accurately in a stream where numbers and characters are intermixed.

This means when you want to ensure capturing everything, including whitespace, you should opt for manual handling by intentionally using functions like `cin.get()` to read exactly what you need. This ensures that `cin` does not skip over any crucial character data because of its default behavior.

input extraction

Input extraction using the `cin` stream involves obtaining and parsing input into the program's variables. By default, `cin` uses the `>>` operator to extract data from the input buffer until it encounters a delimiter, which by default includes whitespace.

In extraction, the data type of the variable is significant. If the input doesn’t match the expected data type, `cin` may leave the variable unchanged or might go into a fail state, stopping further input operations. Consider `cin >> num1 >> symbol;`, where `cin` first tries to extract a number for num1 and then a character for symbol; this parsing process heavily depends on correctly understanding how `cin` interprets and assigns data types.

To manipulate how input is read and interpreted, manual extraction through specific functions, such as `cin.get()`, is used when default behavior of `cin` won’t suffice. This provides more control over how and what data to consider from a mixed or complex input stream.