Welcome to C

1
Welcome to C

• Fundamentals
• Variables and Constants
• C basic Data Types
• Assignments
• Character Arrays
• Preprocessor Directives
• Input and output

2
Why C?

• C is the common denominator of many of todays
  languages
• Cs strong points
• very efficient
• weakly typed language
• Small structured language with many operators
• Has no input/output statements! It uses function
  calls
• hardware independence

• Originated at Bell Labs, Dennis Ritchie 1972
  implemented
• Development language for UNIX operating system

3
C Standard Library

• C programs consist of functions
• Most C programmers take advantage of existing
  functions in the C standard library
• Learn the C language
• Learn how to use the library avoid reinventing
  the wheel
• Your program building blocks
• Functions you write yourself
• Library functions (enhance the portability of
  your program)

4
The C Programming Process

• Design your solution
• Inputs, outputs and logical steps to achieve the
  outputs
• Test your solution
• Code your solution
• Compile Edit your program
• Handling errors
• Run and Test your program

5
Before and after Compilation

• Editor editing your source file
• Compiler routes your program first through
  Preprocessor (pre-compiler) to prepare it for
  compilation. The compiler produces object code
• Linker the compiler sends runtime information
  (such as memory addresses) or combines several
  compiled programs into one executable file
• Your program is loaded to memory to Execute and
  test and perhaps re-edit, re-compile,

6
Studying an outline

• include ltstdio.hgt
• main()
• Code
• goes
• here
• Multiple procedures and
• blocks are optional
• depending on the programs
• requirements

A procedure name
Preprocessor Directives go here
A block
7
Studying a Program

• / First.c This is a sample program. It doesnt
  do much /
• include ltstdio.hgt / To use the functions in
  that library /
• int main() / All C programs require this line
  and the braces /
• int i, j / These 3 lines declare 4 variables
  /
• char c
• float x
• i 4 / i and j are assigned integer values
  /
• j i 7
• c A / All character constants are
  enclosed in single quotes/
• x 9.087 / x requires a floating-point value
  since it was declared as a floating-point
  variable /
• x x 4.5 / change what was in x with a
  formula /
• / Sends the values of the variables to the
  screen /
• printf(d d c f, i, j, c, x)
• return 0 / End programs and functions with
  return /

Output 4 11 A 40.891499
8
The format of a C program

• Readability is IMPORTANT
• Use white space to make programs readable
• Use Comments to explain whats going on to you
  (later) and other programmers
• / any mixture of characters in upper or lower
  case /
• // A newer way to write comments
• DO NOT nest comments
• / start comment 1 / comment 2 / finish comment
  1 /
• UPPERCASE and lowercase
• the entire C language is lowercase
• C programmers reserve UPPERCASE for some names
  (like constants)

• include ltstdio.hgt/ To use the functions in that
  library /
• main() / All C programs require this line and
  the braces /
• int i, j / These 3 lines declare 4 variables
  / char cfloat x i 4 / i and j are assigned
  integer values /
• j i 7c A / All character constants
  are enclosed in single quotes/
• x 9.087 / x requires a floating-point value
  since it was declared as a floating-point
  variable / x x 4.5 / change what was in x
  with a formula // Sends the values of the
  variables to the screen /printf(d d c f,
  i, j, c, x)return 0 / End programs and
  functions with return /

9
Makeup of Programs
Always ends with a semi colon

• Data
• Variables a box in memory that hold data that
  change in the program
• Number
• Character
• Constants any number, character, word or
  phrase a constant does not change
• Character-based
• A
• May
• Number-based
• 10
• -3.4

• Commands
• Declarations char c
• Declares a character variable called c
• Assignments j i 7
• Adds 7 to the variables is value
• function calls
• printf(d d c f, i, j, c, x)
• Sends output to the screen.
• sqrt(16)
• obtains the sqrt of 16
• Other statements such as
• return 0 / exit a function /

10
Data Processing with C Variables and
Constants

• Data types Cs 4 main types
• int 45 -932 0 12
• char A B C
• float 45.12 -322.22 0.00 .4356
• Double 45.0123456789
• Naming conventions
• Unique names
• Begins with a letter, then any letter, digit or
  underscore ( _ )
• Meaningful names - NOT keywords, function names
  or commands

• Declaring and assigning values
• Position (unless global
• after the opening brace of a block of code
  (usually at the top of a function)
• before a function name (such as before main() in
  the program)
• Attributes
• Name age salary first_name
• Type/Size int float char
• Value 20 1500.00 Name here

aggregate type
11
Declaring variables - type

• char variables hold only one character
• int hold whole numbers
• float and double (double precision) hold numbers
  that contain decimal points
• Same precedence as in Maths
• C has many more operators

• State type and name(s), and initial values
  (optional)
• int i
• char a, b, c
• Assign or initialize variables using values that
  have a matching type to that of the declared name
• i 4
• j i 7 // j must be of type int

Primary math operators Add - Subtract Multi
ply / Divide
12
Declaring variables - position

• global variables
• include ltstdio.hgt
• int num100 / declaration of global
  variable FORBIDDEN !! /
• int main()
• printf("Global value is d", num)
• //d means print a decimal value
• return 0

• local variables
• include ltstdio.hgt
• int main()
• int num10 / declaration of local variable /
• printf(Local value is d", num)
• return 0

Prints 10
Prints 100
13
Declaring variables quantifiers

• Quantifiers such as long, short, signed and
  unsigned could be applied to these basic data
  types
• short keyword can be used with int to indicate a
  short integer (usually the range of values for
  int are at least the same as for short and less
  than long
• long keyword can precede an int or double to
  indicate that the number being stored is longer
  than usual
• unsigned extra storage range
• signed if your data contains negative values
  less range
• C does not have a string-type variable you need
  an aggregate variable type that combine other
  fundamental types, e.g. array (later!)
• Complex data types include enumerations, arrays,
  structures, unions, lists, stacks, queues, trees
• Pointers are a special data type that can hold a
  memory address

14
C Data Types
Minimum ranges that are used follows ANSI C
standard
15
Assigning Values to variables

• An assignment statement take the form
• variable expression

A name you declared earlier
Any variable, constant, expression, or
combination
produces a result that is the same data type as
the variables
main() char first, middle, last int
age float salary first A middle
B last C age 28 salary
25000.00 // Rest of the program
You can assign variables or mathematical
expressions to other variables, e.g.
payable_tax salary tax_rate Do not mix
types in assignments, e.g. middle 123.45 //
Do not do this!
Do not put commas
16
L-Value R-Value

• L-values
• Expressions that can appear on left side of
  equation
• Can be changed (i.e., variables)
• e.g. x 4
• R-values
• Only appear on right side of equation
• Constants, such as numbers (i.e. cannot write 4
  x)
• L-values can be used as R-values, but NOT vice
  versa

17
char and int in C

• Integers and character variables can be used
  interchangeably
• Each ASCII character has a unique identification
  number
• char ch
• ch T 5 // Add 5 to the ASCII character.
• The ASCII value of T is 84.
• 84 5 89
• The value Y in c.
• int i P // Assigns the value 80 to i

18
Constants
Literal constant

• include ltstdio.hgt
• main()
• const float PI 3.141593
• float diameter, radius, circ, area
• printf("\nEnter the diameter of a ")
• printf(" circle in mm ")
• scanf("f", diameter)
• circ PI diameter
• radius diameter / 2.0
• area PI (radius radius)
• printf("\tIts circumference is .2f mm\n",
  circ)
• printf("\tAnd its area is .2f sq.mm\n ", area)
• return 0

• Constants are declared using const keyword
• Symbolic Constants are defined in the
  preprocessor area of the program, declared using

define CONSTANT_NAME Value
19
Constants

• Literal Constants
• int base10 decimal whole number without a
  decimal point, e.g. 65535
• Octal in base8 e.g. 177777
• Hexadecimal in base16 e.g. 0xFFFF
• float a number that contains a fractional
  portion
• char a single character enclosed in single
  quotation marks, e.g. A

• String Constants
• Anything enclosed in double quotation marks,
  e.g.C Programming

In memory, the length of C is 2, Hello is 6
20
String Constants

• Is always enclosed in double quotation marks,
  examples
• C Program 123 62 Independence
  Sq. x
• Any group of characters, digits and punctuation.

• All string constants end with a NULL character.
  You do not see the \0, but C makes sure it
  stores the NULL character at the end of the
  string in memory.
• This is how C can tell the end of a string.

21
Introducing Arrays

• Suppose you want to hold the name, age and salary
  in variables
• age and salary are easy because there are
  variable types that can hold such data
• int age
• float salary
• For name you need many character variables next
  to each other in memory a character array
• char name15
• An array declaration always includes brackets (
  ) that declare the storage C needs to reserve
  for the array
• This declaration reserves 15 character spaces
  therefore length of name can be anything up to
  14 characters (we will see why that is the case)

22
Initializing Character Arrays

• Using a string literal
• char name Michael Jones
• C will count the strings length, adds one for
  the null zero
• This statement will reserve space for 14
  characters (13 characters in addition to the Cs
  string terminating symbol - Null Zero
• Using individual characters
• char name M,i,c,h,a,e,l,
  ,J,o,n,e,s,\0
• Create an array capable of holding a specific
  number of characters
• char name15
• This statement will reserve 15 spaces including
  the Null Zero
• Names that can be stored in this array cannot
  exceed 14 characters
• Declare with Missing information no size and
  array is not initialized!
• char name /does nothing/
• C will assume that this array contains zero
  elements

23
Assigning values to Arrays
In memory

• Declaring the size
• char name15 Michael Jones
• This reserves 15 spaces to hold names up to 14
  characters long the 15th space is the Null Zero
• Each of the 15 boxes of the array is called an
  element.
• Notice the null zero (the string terminating
  character) at the end of the string.
• Notice also that the last character of the array
  contains no data
• You must reserve enough space for your data
• char name5 Michael Jones
• /not enough/

24
Access to individual array elements

• You can access the array as a whole or single
  elements of it
• You can assign values to the individual array
  elements by putting the elements location,
  called the subscript, in brackets, as follows
• name3 k / overwrites the h (at subscript
  3) in the name Michael with a k /
• All array subscripts start at zero - assigning
  name3 changes the fourth element In the array

• You can use the subscript notation to assign
  initial values to an array later in the program
• name0 first char
• name1 second char
• name2 third char
• name13 last char
• name14\0 /Needed to ensure this is a
  string/

25
The strcpy() function

• is a built-in function in string.h standard
  library like printf() in stdio.h that allows
  you to copy a string constant into a string.
• To copy Michael Jones into name, you would
  type
• strcpy(name, Michael Jones)
• first value in the parenthesis is a character
  array name (must be long enough to hold the
  string), and that the second value is a valid
  string constant or another character array that
  holds a string

26
Preprocessor Directives

• commands to the preprocessor - typically placed
  at column 1 at the top of your program
• include ltstdio.hgt
• main()
• begin with a hash sign () - Never put a
  semicolon at the end of the preprocessor
  directives because they are pre-processor
  commands and not C commands
• The include preprocessor directive merges a disk
  file into your source program.  
• include ltfilenamegt / The search for the file is
  performed in an implementation-dependent
  manner i.e. in pre- designated directories /
•  or
• include filename / The pre-processor searches
  in the same directory as the file being
  compiled for the file to be included /

27
The include directive

• Suppose you print your name and address often in
  your C programs using the following lines
• printf(Akil Wamucia\n)
• printf(Apartment 2\n)
• printf(233 Atlantic Way\n)
• printf(St. Andrew\n)
• printf(Barbados\n)
• Instead of typing this every time!
• save them in a file called myadd.c. from then on,
  you would only need to type the single line
• include ltmyadd.cgt

• The include directive is mostly used to include
  special programs called header files (using a .h
  extension) that come with your C compiler
• The most common header file is named stdio.h
  (standard input/output header) that gives your
  compiler needed information about built-in
  routines that perform input and output such as
  the printf().

28
The define directive

• works in exactly the same way as the
  search-and-replace command found in word
  processors
• define ARGUMENT1 ARGUMENT2
• ARGUMENT1 is a single word with no spaces
• ARGUMENT2 can be any character, word or phrase
• The define directive replaces all occurrences of
  ARGUMENT1 in your program with the contents of
  ARGUMENT2 before compilation
• ARGUMENT1 is NOT a variable
• Saves memory
• Easy modification to programs

29
Input and output

• The printf() function and its optional arguments
• basic screen output function
• Control Strings
• Conversion Specifiers
• Escape Sequence
• Modifying Conversion Characters
• The scanf() function
• basic keyboard input function

30
The printf() function

• A C library function in the ltstdio.hgt library.
  Sends data to the standard output device (screen)
  unless you redirect the standard output to a
  different device , using the format
• printf(control_string , one or more values)
• The control \ format string contains
• Literal text is printed as is without variation
• printf(Your Text)
• Escaped sequences special characters preceded
  by \
• printf(Text on first line\nText on second
  line)
• Conversion specifiers followed by a single
  character
• Indicates (usually) that a variable is to be
  printed at this location in the output stream.
• printf(c d f, a_char_var, an_integer_var,
  a_float_var)
• All together
• printf(character c integer d float f,
  a_char_var, an_integer_var, a_float_var)
• The variables to be printed must appear in the
  parameters to printf following the format string,
  in the order that they appear in the format
  string.

optional
31
Escape Sequence
32
Escape Sequence

• To print two names on two different lines,
  include \n between them
• printf(Harry or\nJerry\?)
• This program rings a bell on your computer by
  assigning the \a escape sequence to a variable
  and then printing that variable
• //This program rings a bell.
• include ltstdio.hgt
• main()
• char bell \a
• printf(c, bell) //c means print a
  character value
• return

Harry or Jerry?
To print a question mark at the end of the second
line
33
Conversion Specifiers

• There must be one conversion specifier for each
  argument being printed out!
• Ensure you use the correct specifier for the type
  of data you are printing!

34
What would this program print?

• include ltstdio.hgt
• int main()
• int ten10,x42
• char ch1'o', ch2'f'
• printf("d cc d is f\n",ten,ch1,ch2,x,
  1.0x / ten )
• return 0

Why do we need to do this? We will talk about a
better way later.
35
Conversion Specifiers Modifiers

• floating-point numbers (using f) print with too
  many decimal places for most applications
• insert a modifying number inside to tell C how
  many positions to print

prints

• many C programmers ignore the width specifier
  part and specify only the decimal part as in
  .2f.
• Similarly, the width of strings can be
  controlled. Use the width modifier in the s
  string conversion character - if you do not
  specify enough width to output the full string, C
  ignores your width

36
Keep Count of Output

• your printed values must match the control_string
  supplied with them
• printf("The result is d and d\n", a, b)
• A mismatched value will produce garbage with ONE
  exception
• printf(c, 65) // Prints letter A
• printf(d, A) // Prints the number 65

37
The scanf() function

• A C library function in the ltstdio.hgt library
• one way to get input from the keyboard
• Uses a similar format as printf()
• scanf(control_string , one or more values)
• Uses same conversion specifiers EXCEPT
• never include the newline character ( \n ) with a
  scanf() control_string as the function knows
  that the input is finished with the user presses
  Enter ?
• Another problem with scanf()
• requires the use of pointer variables this will
  become clear when you learn pointers
• For now, Always remember to put an ampersand (
  ) before variable names inside a scanf()
• scanf(d, anInteger) //anInteger is declared
  as int

38
The scanf() function

• Reading more than one variables in one time
• int n1,n2
• float f
• scanf("ddf",n1,n2,f)
• requires that your user type the input exactly
  the way the control_string specifies!
• You can use other characters to separate the
  numbers
• scanf("valued,ratiof", value,ratio)
• You must provide input like value27,ratio0.8
• You cannot control your users typing. If
  incorrect data is entered there is not much you
  can do apart from verifying it.
• If you are reading into a long or a double, you
  must precede the conversion specifier with an l
  (a lower case L)

39
Reading Long numbers

• int main()
• int x
• long y
• float a
• double b
• scanf("d ld f lf", x, y, a, b)
• return 0

40
Printing Arrays

• You can print the entire string (or array) by
  using s conversion specifier
• printf(s, name) / do not put the brackets
  after the array name /
• you can print it with or without the (s the
  string format code).
• printf(name)
• You can input a string from the keyboard using
• scanf(s, name)