and Compiling Compiler Errors
(continued)
The Central Processing Unit
A CPU is on a chip called a microprocessor
It continuously follows the fetch-decode-execute
cycle:
Retrieve an instruction from main memory
fetch
execute
Carry out the
instruction
decode
Determine what the
instruction is
Secondary Memory Devices
Secondary memory
devices provide
long-term storage
Hard disks
Floppy disks
ZIP disks
Writable CDs
Writable
DVDs
Tapes
Central
Processing
Unit
Information is moved
between main memory
and secondary memory
as needed
Hard Disk
Main
Memory
Floppy Disk
Input / Output Devices
Monitor
Keyboard
Monitor screen
Keyboard
Mouse
Joystick
Bar code scanner
Touch screen
Central
Processing
Unit
I/O devices facilitate
user interaction
Hard Disk
Main
Memory
Floppy Disk
Flow of Information During Program Execution
(stored program concept)
[Figure 1.13 in the textbook]
Program Development
The mechanics of developing a program include
several activities
writing the program in a specific programming language
translating the program into a form that the computer can
execute
investigating and fixing various types of errors that can
occur
Software tools can be used to help with all parts of
this process
Entering, Translating, and Running
a High-Level Language Program
[Figure 1.12 in the textbook]
Basic Program Development
Edit and
save program
errors
errors
Compile program
Execute and
evaluate program results
Errors (a.k.a., bugs)
A program can have three types of errors
The compiler will find syntax errors and other
basic problems (compile-time errors)
If compile-time errors exist, an executable version of the
program is not created
A problem can occur during program execution,
such as trying to divide by zero, which causes a
program to terminate abnormally (run-time errors)
A program may run, but produce incorrect results,
perhaps using an incorrect formula (logical errors)
The first bug!
Read more at:
http://www.history.navy.mil/photos/pers-us/uspers-h/g-hoppr.htm
Programming Languages
Each type of CPU executes only a particular
machine language
A program must be translated into machine
language before it can be executed
A compiler is a software tool which translates
source code into a specific target language
Often, that target language is the machine
language for a particular CPU type
Syntax and Semantics
The syntax rules of a language define how we can
put together symbols, reserved words, and
identifiers to make a valid program
The semantics of a program statement define what
that statement means (its purpose or role in a
program)
A program that is syntactically correct is not
necessarily logically (semantically) correct
A program will always do what we tell it to do, not
what we meant to tell it to do
Questions?