Download notes - Department of Computer Science

COM S 207
Basic Concepts: computer, program,
programming …
Instructor: Ying Cai
Department of Computer Science
Iowa State University
[email protected]
In the beginning
Everything in computer is coded as 0 and 1
lowercase "a"  1100001
integer 20  10100
What is computer about
8-bit, 16-bit, 32-bit, 64-bit CPU?
Computer Anatomy
Program
A sequence of instructions for a computer to
execute



All instructions are encoded into a string of 0/1
Program = stored instruction
Program = CODE + data
Programming
The act of writing programs
Programming language
Machine language



Computers use the alphabet 0
and 1 ONLY.
Instructions are built from
combinations of 0 and 1!
Example
 00101000 00000001 00000010
 might mean ADD 1 and 2
Programming language
Assembly language


Still machine language alike, but more readable
Example: ADD 1 and 2  00101000 00000001 00000010
Programming language
High-level language: English-like languages





FORTRAN, COBOL, Pascal, Basic, C, Icon
C++, Java, ML
Scheme, Lisp,
Prolog
Perl, Python, Ruby
Language Elements
Data types


Primitive (integer, character, double, boolean, etc.)
Constructed (string, list, array, object, etc.)
Decision (if, switch, etc.)
Loop (for, while, until, etc.)
To write a program, it is
critical that you understand
the syntax and semantics of
each instruction (also called
statement).
Compiler
Convert a program into machine language instructions
that can be executed by a computer
Compiler
Platform dependency
In general, different languages and platforms need
different compilers
 Portability and convenience are issues
Compiler for Unix
Compiler for Linux
:::
Compiler for Mac
Java Virtual Machine
A virtual machine that can execute Java binary code
Java Compiler
Convert a program into machine language
instructions that can be executed by a
computer
Tools
Editor: allows you to enter and edit instructions

Programmer converts pseudo-code (which he understands) to
java code (something java compiler can understand)
Compiler

Converts java code (something java compiler can understand)
to class files (something that a Java Virtual Machine can
understand)
JVM (Java Virtual Machine): executes/runs class files
Debugger


Allows you to have the JVM execute one instruction at a time
and lets you see what is going on during the execution.
This will help you to find runtime errors.
Tools
Integrated Development Environment (IDE):
(e.g., Eclipse)

has all above tools integrated into one tool.