Why is symbol table a necessary tool during compilation?

Answer 1

Symbol Table is important in compilation.

The first step of compilation is lexical analysis. This produces tokens, the attributes of which (eg. name, data type etc.) are stored on the symbol table.

The next step is syntactic analysis, wherein a hierarchical structure is lent to the stream of tokens making use of the grammar of the language. This step is often combined in a single pass with semantic analysis as well.

It is semantic analysis phase and the later code generation scheme that makes use of the symbol table. Semantics are a set of logical rules that can be applied to tokens only if their attributes are known. So, it is here that the need to refer a symbol table arises.