Steps for Compiling and executing the Programs

Steps for Compiling and executing the Programs

A compiler is a software program that analyzes a program developed in a particular
computer language and then translates it into a form that is suitable for execution
on a particular computer system. Figure below shows the steps that are involved in
entering, compiling, and executing a
computer program developed in the C programming language and the typical Unix
commands that would be entered from the command line.
Step 1: The program that is to be compiled is first typed into a file on the
computer system. There are various conventions that are used for naming files,
typically be any name provided the last two characters are “.c” or file with
extension .c. So, the file name prog1.c might be a valid filename for a C program.
A text editor is usually used to enter the C program into a file. For example, vi is a
popular text editor used on Unix systems. The program that is entered into the file
is known as the source program because it represents the original form of the
program expressed in the C language.

Step 2: After the source program has been entered into a file, then proceed to have
it compiled. The compilation process is initiated by typing a special command on
the system. When this command is entered, the name of the file that contains the
source program must also be specified. For example, under Unix, the command to
initiate program compilation is called cc. If we are using the popular GNU C
compiler, the command we use is gcc.
Typing the line
gcc prog1.c or cc prog1.c
In the first step of the compilation process, the compiler examines each program
statement contained in the source program and checks it to ensure that it conforms
to the syntax and semantics of the language. If any mistakes are discovered by the
compiler during this phase, they are reported to the user and the compilation
process ends right there. The errors then have to be corrected in the source program
(with the use of an editor), and the compilation process must be restarted. Typical
errors reported during this phase of compilation might be due to an expression that
has unbalanced parentheses (syntactic error), or due to the use of a variable that is
not “defined” (semantic error).

Step 3: When all the syntactic and semantic errors have been removed from the
program, the compiler then proceeds to take each statement of the program and
translate it into a “lower” form that is equivalent to assembly language program
needed to perform the identical task.
Step 4: After the program has been translated the next step in the compilation
process is to translate the assembly language statements into actual machine
instructions. The assembler takes each assembly language statement and converts it
into a binary format known as object code, which is then written into another file
on the system. This file has the same name as the source file under Unix, with the
last letter an “o” (for object) instead of a “c”.
Step 5: After the program has been translated into object code, it is ready to be
linked. This process is once again performed automatically whenever the cc or gcc
command is issued under Unix. The purpose of the linking phase is to get the
program into a final form for execution on the computer.
If the program uses other programs that were previously
processed by the compiler, then during this phase the programs are linked together.
Programs that are used from the system’s program library are also searched and
linked together with the object program during this phase.
The process of compiling and linking a program is often called building.
The final linked file, which is in an executable object code format, is stored in
another file on the system, ready to be run or executed. Under Unix, this file is
called a.out by default. Under Windows, the executable file usually has the same
name as the source file, with the c extension replaced by an exe extension.