When a variable is not declared, which type of error is likely to occur?

When a variable is not declared in a programming context, a syntax error is likely to occur. This type of error arises during the compilation phase, where the programming language's compiler checks for the correctness of the code before it is executed.

In many programming languages, every variable must be declared before it can be used. If a variable is referenced without a declaration, the compiler will not recognize it, leading to a syntax error. This error indicates that there is a problem with the structure of the code, making it impossible for the compiler to understand and compile the program correctly.

Logic errors occur when the program runs without crashing but produces incorrect results due to flaws in the program's logic. Run-time errors happen during execution, often due to invalid operations, such as dividing by zero. Compile errors, while similar to syntax errors, specifically refer to errors that are related to incorrect code that prevents compilation but do not directly imply that a variable declaration is missing.

Hence, in this context, when a variable is not declared before use, it is primarily a syntax error that is encountered first, as the program cannot progress to execution until all syntax issues are resolved.