What error is present in the variable declaration of the following C program?

The correct choice points out a common issue related to variable naming conventions in C programming. In the C language, variable names must adhere to specific rules, which include not starting with a digit, avoiding special characters such as hyphens, and not including spaces.

If the declaration of the variable includes a hyphen (which is often confused with the minus operator), it would result in an invalid variable name. Since hyphens are not allowed in identifiers, this would prevent the program from compiling correctly, leading to no output being generated when the variable is referenced.

Understanding this rule is crucial for writing syntactically correct C code. Even if everything else in the code is functioning correctly, an issue in variable names can halt the compilation process altogether, making it impossible for the program to produce any output. Thus, discerning that the presence of a hyphen is indeed an error helps solidify the importance of adhering to naming conventions in programming.