Question

Which of the following are valid C++ assignment statements? Assume that i, x, and percent are double variables. a. i = i + 5; b. x + 2 = x; c. x = 2.5 *x; d. percent = 10%;

Short answer

Statements (a) and (c) are valid; (b) and (d) are invalid.

Step-by-step solution

Analyzing Statement (a)

The statement (a) `i = i + 5;` seeks to assign the value of `i + 5` back to the variable `i`. Since `i` is a double, the operation `i + 5` is valid and can be stored back into `i` because it is a valid arithmetic operation and assignment.

Analyzing Statement (b)

The statement (b) `x + 2 = x;` tries to set `x + 2` equal to `x`. In C++, the left side of an assignment must be a modifiable lvalue (i.e., a variable), but `x + 2` is not a modifiable lvalue. Therefore, this statement is invalid.

Analyzing Statement (c)

The statement (c) `x = 2.5 * x;` assigns the result of the expression `2.5 * x` back to the variable `x`. Both the expression and the assignment are valid because `x` is a double, and performing arithmetic operations with it is permitted.

Analyzing Statement (d)

The statement (d) `percent = 10%;` tries to assign `10%` to `percent`. In C++, `%` is the modulus operator and cannot be used with floating point numbers. Additionally, `10%` is not a valid numeric expression, so this statement is invalid.

Key concepts

lvalue and rvalue

In C++, understanding the concepts of lvalue and rvalue is crucial for mastering variable assignments. An lvalue (locator value) refers to an object that occupies some identifiable location in memory (for example, a variable). This means an lvalue has a persistent state, such as the value stored in a variable, enabling it to appear on the left-hand side of an assignment.

In contrast, an rvalue (right value) is any value that does not have a distinct memory location. It is often a temporary value generated by expressions like constants or the result of computations. For instance, in the expression `x = i + 5`, `i + 5` is an rvalue because it is the temporary result of adding the constant `5` to `i`.

A key rule in C++ is that the left-hand side of an assignment must always be an lvalue because it has to represent a modifiable storage location.

arithmetic operations

Arithmetic operations are fundamental in C++ programming, allowing you to carry out basic mathematical computations. These operations include addition, subtraction, multiplication, and division. C++ supports arithmetic on different types of data, such as integers and floating-point numbers.

When performing arithmetic operations on floating-point numbers, like doubles, you achieve a high degree of precision, which is crucial for scientific and financial calculations. For example, the operation `x = 2.5 * x` is perfectly valid with a double type because the multiplication of `2.5` with a variable `x` results in a floating-point value that `x` can then take on.

Ensure that arithmetic expressions are logically correct and involve compatible data types. This prevents unintended rounding or truncation errors, especially important when dealing with floating-point operations.

modulus operator

The modulus operator in C++ has a specific function: it returns the remainder of a division operation between two integers. It is represented by the symbol `%`. For example, in the expression `7 % 3`, the result is `1`, because `3` goes into `7` twice with a remainder of `1`.

Crucially, the modulus operator is not applicable to floating-point data types, like floats or doubles, because these types represent non-integral values. Attempting to use a statement like `percent = 10%` is invalid in C++ as it mistakenly uses a modulus operation with a floating-point type, leading to a compilation error. To perform similar operations with floating-point numbers, consider alternative approaches, like utilizing fmod from the `` library, which allows finding the remainder of floating-point divisions.

variable types in C++

C++ is a strongly-typed language, meaning every variable must have a declared type. This type determines the size and layout of the variable's memory, the range of values the variable can take, and the set of operations that can be applied to it.

Common variable types include:

• int: Holds integer values.
• double: Holds floating-point numbers, providing double the precision of a float.
• char: Used for individual characters.
• bool: Represents Boolean values true or false.

When dealing with assignment operations and mathematical computations, it's important to choose the appropriate type. For instance, a `double` is suitable when you need to store numbers with decimal points and need a higher degree of precision than provided by a `float`.

Understanding how different types interact is key, especially when performing type conversions or dealing with operations that involve multiple types. Ensuring that you're using compatible types can prevent errors and unexpected behaviors in your code.