CPS 196 Introduction to Computer Programming: C

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CPS 196Introduction to Computer Programming C

• Norka Lucena
• norka_at_ecs.syr.edu
• Summer Session II
• Syracuse University
• July 2004

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Overview

• Course setup
• Basics of programming
• Introduction to C
• Variables
• Identifiers

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What is a Computer Program?

• A sequence of instructions used to operate a
  computer to produce specific results

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What is Programming?

• The process of writing those instructions in a
  language that the computer can respond and other
  programmers can understand

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What is a Programming Language?

• The set of instructions that can be used to
  construct a program

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How do programs run?
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What is an Algorithm?

• A step-by-step sequence of instructions that
  describes how to perform a computation
• Example
• Add the numbers from 1 to 100

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Algorithms for Adding the Numbers from 1 to 100
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What is Pseudo Code?

• English phrases used to describe the algorithm
  (the processing steps)
• Example
• Calculate the average of 3 numbers
• Input the three numbers
• Add the three numbers and dividing the sum by 3
• Display the average

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What is a Flowchart?

• The graphical representation of a pseudo code
  employing specifically designed shapes

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Flowchart Symbols
Terminal
Decision
Input/Output
Loop
Predefined Process
Process
Flow Lines
Connector
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Flowchart for Calculating the Average of Three
Numbers
Start

• Input the three numbers
• Add the three numbers and dividing the sum by 3
• Display the average

Input three values
Calculate average
Display average
End
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What is Coding?

• Converting an algorithm into a computer program,
  using a language like C is called coding the
  algorithm

List Requirements
Select an Algorithm
Translate the Algorithm into C language code
Coding
Compiler (Translation Program)
C language source program
Program Translation
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What is C?

• Developed in the 1970s at ATT laboratories
• Names CPL ? BCPL ? B ? C
• Originally created for systems programming, i.e.,
  writing software that controls hardware and other
  software. UNIX and other operating systems are
  written in C
• C was developed to find a common language for a
  variety of application

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What type of language C is?

• C is a high-level language
• A high level language is designed to give better
  programming efficiency i.e. for faster program
  development. C is similar to other high-level
  languages like Pascal, PL/I, FORTRAN and BASIC
• C is a low-level language
• A low level language is designed to give a better
  machine efficiency i.e. faster program execution.
  C is similar to other low-level languages like
  Assembly language and machine language
• C is between both categories, so it is often
  called a middle-level language

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Why do we want to learn C?

• Supports writing portable programs
• A program's source code is portable which can be
  run on various operating environments
• Still high-level language of choice for system
  programming
• Used to write sophisticated workstations and PC
  applications
• Examples Most popular word processors,
  spreadsheets, data base management systems
  and graphics packages are written at least
  partially in C
• Many commercial tools and code libraries support
  C
• C programs are simple and easy to use
• There exist a lot of public domain C code
  available through the Internet

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Why dont we have a break now?
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What are Identifiers?

• Names given to various program elements such as
  variables, functions and arrays
• Identifiers consist of letters and digits in any
  order, except that
• The First character must be a letter
• The identifier can be in lowercase or uppercase
• The upper and lower case are interchangeable
• The underscore (_) can be included and it can
  also begin with underscore
• The identifiers should not contain a blank space,
  hyphen or quotes

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Identifiers

• Valid Identifiers
• sum
• Sum
• SuM
• A112
• total_sum
• Invalid Identifiers
• sum quotes() is illegal
• total-sum illegal character ( - )
• total sum blank space should not be there

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What are Variables?

• Labeled block of memory that you can store,
  change and read information from/to
• A variable is an identifier that is used to
  represent some specified type of information
  within the program
• As an identifier, variables follow the naming
  restrictions mentioned above

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Variables

• The basic format for declaring variables is
• data type var, var, ...
• where data type is one of the four basic
  types, an integer, character, float, or double
  type

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Variables

• Examples of variables
• float x ? declares x to be a floating point
  variable
• int k ? declares k to be an integer variable
• char c ? declares c to be a character variable
• char p ? declares p a pointer-to-character
  (string) variable
• int q ? declares q a pointer-to-integer
  variable