Question

Suppose x and y are int variables and z is a double variable. Assume the following input data: 37 86.56 32 What value (if any) is assigned to x, y, and z after each of the following statements executes? (Use the same input for each statement.) a. cin >> x >> y >> z; b. cin >> x >> z >> y; c. cin >> z >> x >> y;

Short answer

a) x = 37, y = 86, z = 32. b) x = 37, z = 86.56, y = 32. c) z = 37.0, x = 86, y = 32.

Step-by-step solution

Analyzing Statement a: cin >> x >> y >> z;

The input sequence given is `37 86.56 32`. When this statement executes, the first `cin` operation assigns the value `37` to `x` as it expects an integer value. Then, `cin` reads `86` from `86.56` and assigns it to the integer variable `y`, discarding the decimal part `.56`. Finally, `cin` assigns the remaining number `32` to the double variable `z`. So, after this statement, `x = 37`, `y = 86`, `z = 32`.

Analyzing Statement b: cin >> x >> z >> y;

For this statement with the same input `37 86.56 32`, `x` is assigned `37` first. Then, `cin` reads the next available input, `86.56`, into the double variable `z`, which can store floating-point numbers, so `z = 86.56`. Finally, the integer `32` is read into `y`. The variable assignments after this sequence are: `x = 37`, `z = 86.56`, `y = 32`.

Analyzing Statement c: cin >> z >> x >> y;

Using the input `37 86.56 32`, the first value `37` is read and stored in `z`, `z = 37.0` (automatically converted to a double). Next, the integer `86` (from `86.56` ignoring the decimal part) is assigned to `x`, `x = 86`. Lastly, `cin` reads `32` into `y`, completing the assignments: `z = 37.0`, `x = 86`, `y = 32`.

Key concepts

Cin

In C++, `cin` is a standard input stream used to read data from the user input, typically the keyboard. The `cin` object is used with the stream extraction operator (`>>`) to get input values and store them in variables. The process is straightforward: the order in which variables appear after `cin >>` dictates the sequence of input data assignments.

Let's explore how `cin` interprets input for different data types. The way `cin` works is that it reads the user input text until it encounters whitespace (like spaces or newlines), and tries to convert this text to the type expected by each variable.

• For example, if you enter "42 3.14 hello", and your variables are in the order of an int, a double, and a string, respectively, `cin` will assign `42` to the int, `3.14` to the double, and then attempts to assign "hello" to the string variable.
• If the input does not match the expected data type (like attempting to input a string into an int), `cin` will enter a fail state and stop input processing until it’s cleared.

Using `cin` requires understanding not only the order of input but the expected data types to avoid unexpected results. Always ensure your inputs match what each variable expects in the sequence defined.

Data Types

In C++, data types define the nature of data that can be stored in a variable. The basic data types include `int`, `double`, `char`, and `bool`, each serving a distinct purpose.

The `int` type is used for whole numbers without any fractional part. It uses a certain amount of memory, often 4 bytes, depending on the system. Because `int` cannot store fractions, when you input a decimal number like `86.56` into an `int`, it truncates to `86`.

`Double`, on the other hand, is used for floating-point numbers, which include a decimal point or fraction part. This makes it suitable for storing values like `86.56` accurately, using typically double the memory of an `int`, allowing a larger range and precision. These properties make `double` ideal for calculations where precision matters, such as scientific computations.

• Moreover, understanding the behavior of these data types helps in managing and manipulating user input effectively.
• For instance, assigning a double value to an int variable results in truncation of the decimal part, thus altering the original input value.

Each data type serves a special purpose and must be used considering the type and precision of data you wish to handle for each specific use case.

Variable Assignment

Variable assignment is a core part of programming in C++, where specific values are stored into variables for later use in the program. When using `cin`, variable assignments occur in the exact order of `cin >>` statements; understanding this sequence is crucial.

The `>>` operator ensures that inputs are assigned to variables in the order specified. For example, if the code reads `cin >> x >> y >> z;`, the first input value gets assigned to `x`, the second to `y`, and the third to `z`. As seen in the input example `37 86.56 32`, processing will sequentially assign these values to the respective variables.

Here are key points about variable assignment:

• It's important to ensure that the variable's data type matches the expected input. This prevents input errors and ensures accurate data storage.
• When assigning values, any mismatch between input and variable type, such as reading a double into an int, leads to truncation or conversion as needed.
• Efficient program operation often hinges on understanding and correctly implementing these variable assignments, ensuring that data is correctly captured and utilized in the program's logical flow.

Variable assignment is fundamental to capturing user input accurately and using data effectively throughout the program. Therefore, plan input sequences carefully to ensure data is assigned to the correct variables.