C Basics

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C Basics
C is a high-level, general purpose,
object-oriented programming language.
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C Basics

• When  executing a program the computer only does
  what you have programmed ,
• no less, but also no more.
• If you forget anything, or the output does not
  look pretty, or the results are incorrect,
  there's nobody to blame
• but yourself.

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C Basics

• The computer understands (long) sequences of 0's
  and 1's, humans only understand a natural
  language such as English.
• Therefore, there is a translation mechanism
  involved when you try to tell the computer what
  you want it to do

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C Basics
TRANSLATION
Compiler
Object code
Source code
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C Basics

• Source code The source code is a text document
  that contains statements written according to the
  rules
• Object code A sequence of 0's and 1's that the
  computer can, in principle, understand (machine
  code).
• A program called the compiler is used to
  translate the source code into object code.
• Executable code Sequence of 0's and 1's,
  consisting of your object code plus any other
  modules (machine code).

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C Basics
TRANSLATION
Other files
Compiler
Linker
Object code
Source code
Executable code
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C Basics

• When you write C programs,
• There are several things to keep in mind
• Your program does exactly and only what you
  define, no more and no less
• C programs execute, from top to bottom
• C programs can use cin to get input from a
  user, and cout to display output
• C programs usually do some computations

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Basic C Rules

• every C program uses certain keywords that have
  special meaning (e.g. int, main, void, return)
• every C program uses certain operators that
  perform specific actions (e.g. , , cin, cout)
• every C program is case-sensitive,(e.g. int is
  different from Int or INT)
• every C program uses curly brackets to group
  statements together
• every C program has a semicolon at the end of
  every instruction almost
• every C program that handles user input and
  output will contain the line include ltiostream.hgt

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Basic C Rules

• almost every C program will contain the lines
  ..   int main(void)         .....
• return 0   

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Declaring Variables

• C provides several different basic data types.
  The most important ones are
• double a decimal number
• int an integer number
• char a single letter or special symbol,
  anything that is on your keyboard

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Declaring Variables

• Example
• double x 
• int X,y, z 
• char d
• C is case-sensitive
• Variable names can not contain spaces. They must
  start with letters, and can contain only letters,
  numbers, and certain special symbols such as an
  "underscore" _.

varName
type
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Assigning values to variables

• Once a variable is declared, you can assign
  values to it.
• varName expression
• Example
• double x
• x 10.0

expression
varName
Note that this operation looks like the math
symbol for equal, but it works differently
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Assigning values to variables

• When you assign an expression to a variable, the
  following happens
• first,
• the value of the right side is computed
• second,
• that computed value is assigned to the variable
  on the left

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Assigning values to variables

• Example
• double x, y
• int i, k
• x 2.8
• y -1.4x
• i 9
• k (i 2) (7 5i)

the value of the right side is computed
computed value is assigned to the variable on the
left
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Assigning values to variables

• Combined Declaration and Assignment
• In C, you can declare a new variable, and at
  the same time assign a value to it (or initialize
  the variable)
• Example
• double x 1.0
• int i 10, j 20
• int k i j

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Defining Constants

• To define a constant in C you preface the type
  of the variable by the keyword const.
• Example
• const double pi 3.1415

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Defining Constants

• A constant
• can not change inside your program.
• usually declared at the beginning of your
  program,
• must be assigned a value at the time you declare
  them.

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• Now we can produce some more interesting programs.

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A sample program

• Task 1 Create a program that asks the user for
  the radius of a disk, then computes the area and
  circumference.

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A sample program

• Stage 0 As usual, our stage-0 program is
• include ltiostream.hgt
• int main()   
• ......  
• return 0

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A sample program

• Stage 1 We use comments to break up our task
  into smaller subtasks
• include ltiostream.hgt
• void main()
•    // get the radius from the user
•    // compute the area
•    // compute the circumference
•    // display the answers

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A sample program

• Stage 2 Now we get into the details of which
  variables and formulas to use
• include ltiostream.hgt
• int main()
• const double pi 3.1415
•    // need a variable r for the radius
• double r
•    // getting the input from the user
•    cin gtgt r
•     // computing the area A pi r2   
• double A pi r2
•    // computing the circumference
•    double C 2 pi r
•     // displaying both answers
•    cout ltlt A
•    cout ltlt C
• return 0

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A sample program

• Stage 2 Now we get into the details of which
  variables and formulas to use
• include ltiostream.hgt
• int main()
•    const double pi 3.1415
• double r,A,C
•    cin gtgt r
•    A pi r2
•    C 2 pi r
•    cout ltlt A
•    cout ltlt C
• return 0

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A sample program

• At this point, we let the compiler tell us if the
  C grammar is correct or not.
• The compiler will tell us the r2 is "unknown",
  so we change that line to
• A pi rr

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A sample program

• Then we compile it again. It will now compile
• So we can link it to produce the executable file.
  
• Finally, we execute the program to test it, and
  we find that everything works, but it does not
  look good.
• So, we'll modify the program inputoutput one
  more time.

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A sample program

• Stage 3 We add some more input/output statements
  to make our program more "appealing" to the user
  
• include ltiostream.hgt
• int main()
•    const double pi 3.1415
• double r,A,C
• cout ltlt "Please enter the radius "
•    cin gtgt r
•    A pi rr
•    C 2 pi r
• cout ltlt "The area is "
•    cout ltlt A
• cout ltlt "The circumference is "  
•    cout ltlt C
• return 0

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A sample program

• Acutally, the last four statements can be linked
  together. Instead of saying
•   
• cout ltlt "The area is "
•    cout ltlt A
•    cout ltlt "The circumference is "  
•   cout ltlt C
• we can also say
• cout ltlt "The area is " ltlt A ltlt " and the
  circumference is " ltlt C

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A sample program

• After changing that, our program will work
  correctly, and produce reasonably nice looking
  results on the screen.
• include ltiostream.hgt
• int main()
•    const double pi 3.1415
• double r,A,C
• cout ltlt "Please enter the radius "
•    cin gtgt r
•    A pi rr
•    C 2 pi r
• cout ltlt "The area is " ltlt A ltlt "The
  circumference is " ltlt C
• return 0

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Software Development

• When creating a program, you usually proceed in
  four distinct stages
• Problem Analysis
• Design
• Coding
• Verification and Validation

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Stage 1 Problem Analysis

• In this stage you analyze what exactly it is that
  your program needs
• In particular, you describe
• all input values,
• i.e. values that must be supplied from outside
  the program
• all constant values,
• i.e. values that are given with the problem
• all output values,
• i.e. values that must be produced as part of the
  solution to the problem
• You should also think about the types of all
  these values.

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Stage 2 Design

• In this stage,
• break up the problem into subtasks in the order
• write the pseudocode, using comments to describe
  the subtasks instead of actually coding it.
• All necessary formulas are part of this stage.

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Stage 3 Coding

• In this stage
• enter the code for your program, following the
  rules that C requires.
• leave the comments from stage 2, and put your
  code after the respective comments.
• The end product of this stage should be a program
  that compiles and links without errors.

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Stage 4 Verification and Validation

• Check if your program works correctly,
• Is the sequence of events correct ?
• Does your program print out enough information to
  guide the user as to what to do and what the
  output means ?

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1.Problem

• Create a program that will compute the volume of
  a sphere, given its radius.

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2.Problem

• You are working as a consultant for a cable
  company. For each installation that is performed
  by the company, there's a 25.00 service charge
  and an additional 2.00 charge per meter of cable
  used.
• They need a program to compute the total income
  per month.
• In other words, if they use 263 meter of cable
  at 27 different locations, they make 1201.00
  income.