Question

Which of the following is not a valid \(\mathrm{C}_{+}+\) variable name? (There may be more than one.) a. i_think_j_am_valid b. i.may_have \(2_{-}\) many_digits_2_be_valid c. -1 start.and_end_with_underscores_ d. I_Have_A_Dollar_sign e. I-AM_LONG_AND_HAVENOLOWER_CASE_LETTERS

Short answer

Options b, c, d, and e are not valid C++ variable names.

Step-by-step solution

- Understand variable naming rules in C++

Variable names in C++ must follow certain rules: 1) They can include letters (both uppercase and lowercase), digits, and underscores. 2) They must not start with a digit. 3) They must not include special characters like hyphens, periods, or spaces. 4) Reserved keywords cannot be used as variable names.

- Examine each option

Evaluate each variable name against the rules stated in Step 1. Identify if any rule is violated in each option.

- Analyze option a: i_think_j_am_valid

This option only includes letters and underscores, and does not start with a digit. This is a valid variable name.

- Analyze option b: i.may_have 2_many_digits_2_be_valid

This option includes a period (dot) and spaces, which are not allowed in variable names. Hence, this is an invalid variable name.

- Analyze option c: -1 start.and_end_with_underscores_

This option starts with a hyphen (dash) and includes a period (dot), which are not valid characters for variable names. Therefore, this is not a valid variable name.

- Analyze option d: I_Have_A_Dollar_sign

This option includes a dollar sign, which is not allowed in variable names. Hence, this is an invalid variable name.

- Analyze option e: I-AM_LONG_AND_HAVENOLOWER_CASE_LETTERS

This option includes hyphens (dashes), which are not allowed in variable names. Hence, this is an invalid variable name.

Key concepts

variable names

In C++, variable names are identifiers used to name different entities such as functions, arrays, and objects. They help in making the code readable and manageable. When naming a variable, you must use a sequence of characters that adheres to specific guidelines. Each variable in C++ is unique and should have a name that clearly indicates its purpose. Choosing meaningful variable names helps in understanding the code better.

syntax rules

C++ has strict syntax rules governing how variable names can be composed. These rules ensure consistency and prevent errors. Here are the primary syntax rules for variable names in C++:
- Only letters (both uppercase and lowercase), digits, and underscores are allowed.
- The variable name must not start with a digit.
- No special characters such as hyphens, periods, or spaces are permitted.
- Reserved keywords (e.g., `int`, `float`, `if`) cannot be used as variable names.
Following these rules helps maintain code clarity and prevents confusion during compilation.

invalid characters in variable names

Invalid characters in variable names can cause compilation errors and unexpected behavior in your C++ programs. Some common examples of invalid characters include:
- Hyphens (e.g., `my-variable`)
- Periods (e.g., `my.variable`)
- Dollar signs (e.g., `price$`)
- Spaces (e.g., `my variable`)
These characters disrupt the way C++ interprets variable names and should always be avoided. Sticking to allowed characters like letters, numbers (not as the starting character), and underscores will ensure your variable names are valid.

C++ programming

C++ is a widely-used programming language known for its performance and flexibility. It is used in various domains such as game development, system programming, and scientific computing.
When working with C++, understanding the rules and best practices, such as proper variable naming, is crucial. Well-named variables contribute to writing clean, maintainable, and error-free code.
As a beginner, remember to:
- Follow the naming rules strictly to avoid syntax errors.
- Use meaningful names for variables to make your code easier to understand.
- Regularly practice writing and reviewing code to become proficient in C++ programming.
By mastering the basics such as variable naming, you build a strong foundation for tackling more complex C++ programming tasks.