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CS101: COMPUTER PROGRAMMINGLecture 1: Introduction to Computer and Programming
Objectives
In this Lecture you will learn about: Overview of PC components The different types of language
Natural Language Formal Language Functional / Imperative Language Programming Languages
C as an imperative language C program at a glance
Overview of PC Components
Section 1
Computer Hardware Components
Components of a PC
Input / Output Devices
Input Devices Accepts information from the user
and transforms it to digital codes that the computer can process
Example: keyboard, mouse, scanner Output Devices
An interface by which the computer conveys the output to the user
Example: monitor, printer
Main Memory
A semiconductor device which stores the information necessary for a program to run.
2 types ROM (Read Only Memory)
Contains information that is necessary for the computer to boot up
The information stays there permanently even when the computer is turned off.
RAM (Random Access Memory) Contains instruction or data needed for a program
to run Got erased when the computer is turned off.
Central Processing Unit (CPU) Does most of the work in executing a program The CPU inside a PC is usually the
microprocessor 3 main parts:
Control Unit Fetch instructions from main memory and put them in
the instruction register ALU (Arithmetic Logic Unit)
Execute arithmetic operations Registers
Temporarily store instructions or data fetched from memory
Storage Devices
A magnetic device used to store a large amount of information.
Store the software components or data needed for the computer to execute its tasks.
Could be “read only” or “writable”. Example: Hard drive, CD ROM, floppy
disks
Network Devices
Connect a computer to the other computers.
Enable the users to access data or execute programs remotely.
Example: modem, Ethernet card
The different types of language
Section 2
Natural language
Our everyday-language; spoken and written Not 100% needed to understand: Depends on circumstances; the context:
“Do you like one ?” doesn't make sense on its own. It needs a situation around it:
someone holding a bouquet of flowers: you might take one
someone pointing to an expensive car: your opinion is asked
someone 'offers' you an oily cloth to sneeze: you don't take it
Semantics and Syntax
Semantics – the meaning of the language within a given context
Syntax - Syntax are the rules to join wordstogether in forming a correct expression or phrase.
In natural languages it is often possible to assemble a sentence in more than one correct ways.
Formal Language
Language with limited, defined, words Each concatenation of words ('phrase') has a
single, clearly defined meaning no (miss-)interpretation possible
Sometimes called “Context Free Language” To 'talk' to a computer; to instruct a
computer; our commands must be 100% clear and correct.
Often there is only a single, correct syntax.
Functional / Imperative Language Functional Language:
Tell what to do, but not how:sum [1...10]
Imperative Language: Tell what to do, but mainly how:
“Take number 1 and add the next number to it; then add the next number to the sum; and so on; until you have reached 10 as number to be added. Then print the sum of all numbers”
What is Programming?
Programming is instructing a computer to do something for you with the help of a programming language
The two roles of a programming language: Technical: It instructs the computer to perform
tasks. Conceptual: It is a framework within which we
organize our ideas about things and processes. In programming, we deal with two kind of things:
Data - representing 'objects' we want to manipulate
Procedures -'descriptions' or 'rules' that define how to manipulate data.
Programming Language
Formal Language used to communicate to a computer.
A programming language contains instructions for the computer to perform a specific action or a specific task: 'Calculate the sum of the numbers from 1 to
10‘ 'Print “I like programming”‘ 'Output the current time'
Programming Language
Can be classified into as a special-purpose and general-purpose programming languages.
Special-purpose : is design for a particular type of application Structured Query Language (SQL)
General-purpose : can be used to obtain solutions for many types of problems Machine Languages Assembly Languages High-Level Languages
Machine Language
The only language that the processor actually 'understands‘
Consists of binary codes: 0 and 1 Example: 00010101
11010001 01001100
Each of the lines above corresponds to a specific task to be done by the processor.
Programming in machine code is difficult and slow since it is difficult to memorize all the instructions.
Mistakes can happen very easily. Processor and Architecture dependent
Assembly Language
Enables machine code to be represented in words and numbers.
Example of a program in assembler language:LOAD A, 9999
LOAD B, 8282
SUB B
MOV C, A
LOAD C, #0002
DIV A, C
STORE A, 7002
Easier to understand and memorize (called Mnemonics), compared to machine code but still quite difficult to use.
Processor and Architecture dependent
High-Level Language
Use more English words. They try to resemble English sentences. Therefore, it is easier to program in these languages.
The programming structure is problem oriented - does not need to know how the computer actually executes the instructions.
Processor independent - the same code can be run on different processors.
Examples: Basic, Fortran, Pascal, Cobol, C, C++, Java
A high level language needs to be analyzed by the compiler and then compiled into machine code so that it can be executed by the processor.
C Programming Language
Why 'C' ? Because based on 'B'; developed at Bell
Laboratories Developed by Dennis Ritchie at Bell Laboratories
in the 1960s In cooperation with Ken Thomson it was used for
Unix systems The C Language was only vaguely defined, not
standardized, so that almost everyone had his own perception of it, to such an extend that an urgent need for a standard code was creeping up
C Programming Language
In 1983, the American National Standards Institute (ANSI) set up X3J11, a Technical Committee to draft a proposal for the ANSI standard, which was approved in 1989 and referred to as the ANSI/ISO 9899 : 1990 or simply the ANSI C, which is now the global standard for C.
This standard was updated in 1999; but there is no compiler yet
C as An Imperative Language
Section 3
C – An Imperative Language
C is a highly imperative language We must tell it exactly how to do what; the means and functions to use; which libraries to use; when to add a new line; when an instruction is finished; in short: everything and anything…
Hint: Observe the syntax in the next slide
C Program at a Glance
Section 4
A Simple Program in C
#include <stdio.h>
int main(){
printf("I like programming in C.\n");return 0;
}
A Simple Program in C - explanation
#include <stdio.h>
int main()
{
printf("I like programming in C.\n");
return 0;
}
standard Library, input-output, header-file
Begin of program
End of statement
End of Segment
Start of Segment
Function for printing text
Insert a new line
C Output
I like programming in C.
Summary
We have looked at some underlying hardware
We have seen some different types of languages; the relevance of semantics and syntax.
We have observed the detail necessary in an imperative language to instruct a computer properly.
Finally, we examined the syntax to print a line of text to the screen of our computer.
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