Introduction to Computer

Programming

Mr. Orfel L. Bejarin,MIT 1

 A microprocessor is designed to “understand” a set
of commands called an “instruction set”
 All instructions must be provided to the CPU in its
native language, called machine language.
 All data transmission, manipulation, storage, and
retrieval is done by the machine using electrical
pulses representing sequences of binary digits.
 If eight-digit binary codes are used, there are 256
numbered instructions from 00000000 to
11111111.

Mr. Orfel L. Bejarin,MIT 11/4/2013 2

 Instructions for adding two numbers would
consist of a sequence of these eight-digit
codes from 00000000 to 11111111.
 Instructions written in this form are referred
to as machine language.
 It is the native language that the CPU
“speaks” and “understands”.
 It is possible to write an entire program in
machine language. However, this is very
time consuming and difficult to read and
understand.

Mr. Orfel L. Bejarin,MIT 3

 Fortunately, special languages have been
developed that are more easily
understood (than machine language).
 These special languages are called
programming languages.
 These languages provide a way to write
computer programs that are understood
by both computers and people.
 Programming languages have their own
vocabulary and rules of usage.
 Some languages are very technical, while
others are similar to English.

Mr. Orfel L. Bejarin,MIT 4

 The programming language that is most
like machine language is assembly
language.
 Assembly language uses letters and
numbers to represent machine language
instructions.
 An assembler is a program that reads the
codes the programmer writes in assembly
language and “assembles” a machine
language program based on those codes.
 However, assembly language is still difficult
to read. Mr. Orfel L. Bejarin,MIT 5
 For example, the machine code for adding
two integers might be:
01000011001110100011110101000001001010110
1000010
 While the assembly language code might be:
LOAD A
ADD B
STORE C
◦ This causes the number in A to be added to the number in
B, and the result is stored for later use in C.

Mr. Orfel L. Bejarin,MIT 6

 Machine Language and Assembly Language
are both called low-level languages.
 In a low-level language, it is necessary for
the programmer to know the instruction set
of the CPU in order to program the
computer.
 Each instruction in a low-level language
corresponds to one or only a few
microprocessor instructions.

Mr. Orfel L. Bejarin,MIT 7

 A high-level language is any programming
language that uses words and symbols to
make it relatively easy to read and write a
computer program.
 In a high-level language, instructions do
not necessarily correspond one-to-one with
the instruction set of the CPU.
 One command in a high-level language may
correspond to many microprocessor
instructions.

Mr. Orfel L. Bejarin,MIT 8

 Many high-level languages have been
developed. These include:
 FORTRAN, COBOL, BASIC, Logo, Pascal, C,
C++, Java, and others.
 These languages simplify even further the
terminology and symbolism necessary for
directing the machine to perform various
manipulations of data.

Mr. Orfel L. Bejarin,MIT 9

 High Level Languages:

◦ Reduce the number of instructions that must be

written.
◦ Allow programs to be written in a shorter amount
of time than a low-level language would take.
◦ Reduce the number of errors that are made,
because…
 The instructions are easier to read.
◦ Are more portable (the programs are easier to
move among computers with different
microprocessors).

Mr. Orfel L. Bejarin,MIT 10

 Low Level Languages:

◦ Instructions can be written to enable the computer

to do anything that the hardware will follow.
◦ Require less memory
◦ Run more quickly

Mr. Orfel L. Bejarin,MIT 11

 Consider the following programs that add two
numbers together:
BASIC Pascal C++ LOGO
10 I = 3 program AddIt; int main( ) to add :I :J :K
20 J = 2 var { MAKE “I :3
30 K = I + J i, j, k : integer; int i, j, k; MAKE “J :2
begin i = 3; MAKE “K :I + :J
i := 3; j = 2; end
j := 2; k = i + j;
k := i + j; return 0;
end. }

Mr. Orfel L. Bejarin,MIT 12

 Programmers writing in a high-level
language enter the program’s instructions
into a text editor.
 The files saved in this format are called
text files.
 A program written in a high-level language
is called source code.
 The programs are translated into machine
language by interpreters or compilers.
 The resulting machine language code is
known as object code.
Mr. Orfel L. Bejarin,MIT 13
 An interpreter is a program that translates
the source code of a high-level language
into machine language.
 Each instruction is interpreted from the
programming language as needed (line by
line of code).
 Every time the program is run, the
interpreter must translate each instruction
again.
 In order to “run” the program, the
interpreter must be loaded into the
computer’s memory. Mr. Orfel L. Bejarin,MIT 14
 A compiler is another program that
translates a high-level language into
machine language.
 A compiler makes the translation once so
that the source code don’t have to be
translated each time the program is run.
◦ The source code is translated into a file called
an object file.
◦ A program called a linker is used to create an
executable program.
◦ Most modern compilers let you compile and
link in a single operation, and have an “IDE”
(Integrated Development Environment) to
enter text, debug, compile, link, and run
programs.
Mr. Orfel L. Bejarin,MIT 15
 Bug: An error in coding or logic that
causes a program to malfunction or to
produce incorrect results.
 Debug: To detect, locate, and correct
logical or syntactical errors in a program.
 Folklore attributes the first use of the
term “bug” to a problem in one of the
first electronic computers that was traced
to a moth caught between the contacts of
a relay in the machine.
http://www.microsoft.com/canada/home/
terms/2.7.1.1_B.asp

Mr. Orfel L. Bejarin,MIT 16