FROM SOURCE CODE TO OUTPUT
All computer programs must be converted / translated / compiled / interpreted into machine
language before the computer's CPU can execute the instructions.
The source program comprises code written in a programming language such as BASIC,
Pascal, C and so on.
Depending on the level of programming language, the corresponding type of Translator will
convert the source code to object code which is stored in the matching language program. This
code is now at the point where the instructions can be executed by the computer to produce the
output.
Types of translators
Source Program
Source Code is the language or words that we use to write the program. Just as English, or
French or Spanish, or German is the language that people use to write with, then Pascal is one
language that is used to write programming code. This code is called Source Code.
The rules of the language (called syntax) must be followed, in our example, it is the Pascal
language.
Again, just as English, and those other languages have their own grammar rules, such as spelling
and sentence construction, Pascal programming language is no different.
So you write your program using the required rules of the language that you are using.
Source code is the programming code that is written in either:


a low-level programming language such as assembly language, or
a high-level programming language such as BASIC, Pascal, C, C++, etc.
Translating the Source Code
Translators are responsible for converting the source code into machine code for the computer to
execute.
The shaded gray areas above show the different types of translators that are used to convert
source code to machine language code.
If the source code was written using:


an assembly language program, then an assembler is needed to convert it to machine
language code
a high-level language program such as Pascal, then either a compiler or an interpreter
could be used for the conversion.
Since we have a choice of a compiler or an interpreter, let us look at these two in more detail:
Comparison of a compiler and an interpreter
Compiler
Interpreter
How is the source
program translated?
The entire program is translated
before execution
Each line of the program is translated and
run before the next programming line is
translated and run
How often is the
source program
translated?
Each line of programming code is
translated once into object code and
kept for execution later
Each line of the source code must be
translated into object code every time the
program is executed (run)
Can the object code
be stored for later
use?
No, the object code must be translated
Yes, the object code can be stored and
from the source code each time it needs to
executed (run) later
be executed (run).
Executing the Object Code
This is the machine language code that can now be executed by the computer to follow the
instructions and produce some output. Sometimes, when a program is compiled, there are various
sub-programs in object code that are created. Before executing the object code, these subprograms must be linked together to form one set of object code.
Maintaining programs
Programs need to be kept up to date, or maintained in order to remain useful. Maintaining a
program can involve adding extra tasks, entering more data of a different form or outputting data
in a different format.
Other examples include a tax rate may need to be changed or a zip code may need to be added.