Which of the following is a legal identifier?
a. 1program
Obiprogram!
c.program 1
d.program_1
The Correct Answer and Explanation is :
The correct answer is d. program_1.
Explanation:
In programming, an identifier is the name used to identify variables, functions, or other user-defined elements in a program. Each programming language has its specific rules for what constitutes a valid identifier. However, most modern programming languages share common guidelines for identifiers:
- The first character must be a letter (a-z, A-Z) or an underscore (
_). It cannot be a digit. - Subsequent characters can include letters, digits (0-9), and underscores.
- Identifiers cannot include spaces, special characters like
!,@, or#. - Identifiers cannot be reserved keywords or language-specific words (like
if,while,class, etc.). - Some languages may enforce case sensitivity (e.g.,
Programandprogramare different in Python).
Now, analyzing each option:
a. 1program
- This is not a legal identifier because it starts with a digit, which violates the rule that the first character must be a letter or underscore.
b. Obiprogram!
- This is not a legal identifier because it contains a special character (
!), which is not allowed in identifiers.
c. program 1
- This is not a legal identifier because it contains a space. Identifiers must not have spaces.
d. program_1
- This is a legal identifier because it starts with a letter (
p), includes only valid characters (letters, digits, and an underscore), and does not contain spaces or special characters.
Why program_1 is valid:
Identifiers like program_1 adhere to the naming conventions of most programming languages. The use of underscores makes it readable, and the combination of letters and digits ensures it is descriptive. It’s a common practice to use underscores to separate words in identifiers, especially when spaces are disallowed.
Thus, program_1 is the only valid identifier among the options provided.