Flex - Bison, early stages of a compiler

Build the early stages of a compiler on flex - bison program. Need help with that More specifically, a source-to-source compiler (trans-compiler or transpiler) will be created, i.e. a type of compiler that takes as input the source code of a program in one programming language and generates the equivalent source code in another programming language. In our case, the source code will be written in the imaginary Theta programming language and the generated code will be in the well-known C programming language.