What are the stages of assembling a source program?

The stages of assembling a source program are preprocessing, compiling, assembling, linking, and loading.

The first stage in assembling a source program is preprocessing. This stage involves the removal of comments and the expansion of macros. The preprocessor also handles the inclusion of header files, which contain declarations of functions and variables that can be used in the program. The preprocessor directives, which are instructions for the preprocessor, are also processed at this stage. These directives can include commands to include other source files, define macros, conditionally compile parts of the program, and others.

The next stage is compiling. The compiler translates the preprocessed source code, which is written in a high-level programming language, into assembly language. The compiler checks the source code for syntax errors and reports any it finds. It also optimises the code to make it run more efficiently. The output of this stage is an assembly language program.

The third stage is assembling. The assembler translates the assembly language program into machine language. The assembler also resolves symbolic names for memory locations and replaces them with actual memory locations. The output of this stage is an object file, which contains machine language instructions and data.

The fourth stage is linking. The linker combines the object file with other object files and library files to create an executable file. The linker resolves references to functions and variables in other object files and libraries. It also determines the memory locations of these functions and variables.

The final stage is loading. The loader loads the executable file into memory so that it can be executed by the computer's processor. The loader also sets up the stack and the heap, which are areas of memory used for temporary storage and dynamic memory allocation, respectively. The loader then transfers control to the start of the program, which begins executing the machine language instructions.

Each of these stages plays a crucial role in transforming a source program written in a high-level language into an executable program that can be run on a computer. Understanding these stages can help you better understand how programs are created and executed.