When the end of the function, or the return statement, is reached the thread of execution returns to the statement immediately following the function call. A compiler takes a source file and makes sense of it. It is the first stage in the conversion of a program into machine code. The compiler will produce an object file which is linked in with other object files and library files to produce the machine code program which is run. A compiler is a large program which is specially written for a particular computer and programming language.
Most compilers work in several phases.
The final phase is the code generator, which produces the object file which is later linked by the linker. A directive is a command of some kind. In C this usually refers to the pre-processor, which acts on these to get particular effects. Some assemblers also support directives which can change the way they work, but these are not the same as the ones used in C. format string The formatted print and scan functions, for example scanf and printf, need to know how to format their output. To tell them the layout we use the format string.