CSE 459'21: Programming in C

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CSE 459.21 Programming in C

• Instructor Na Li
• Email lina_at_cse.ohio-state.edu
• Phone [phone]
• Office DL 274 (Dreese Laboratories)
• Office Hour Tuesday 100--200PM

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Course Information

• Course Page
• http//www.cse.ohio-state.edu/lina/teaching/cse45
  9-21/
• Prerequisite
• cse321 or equivalent
• Textbook
• The C Programming Language, Kernighan Ritchie

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Syllabus

• Lectures
• Chapter 1-8 will be covered.
• Labs
• Four labs
• Electronic submission
• run on stdsun.cse.ohio-state.edu
• lab quality, correctness
• Try to develop good coding style
• Exams
• No exams

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Sample 1

• / Hello World! /
• include ltstdio.hgt
• int main()
• printf(Hello World!\n)
• return 0

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Sample 1 Dissection

• What it has?
• A function definition main
• A line of comment
• A line of preprocessor directive
• An output statement
• A return clause
• What it does?
• Ask the computer to say hello to the world.
• What it does not do?
• It seems not computing!!
• No real work
• not taking input
• does not change any value

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Sample 2

• include ltstdio.hgt
• define MAGIC 10
• int main(void)
• int i0
• int factor, remainder
• while (i lt 3)
• printf(Guess a factor of MAGIC larger
  than 1 ")
• scanf("d, factor)
• remainder MAGIC factor
• if (remainder 0)
• printf(You got it!\n)
• else
• printf(Sorry, You missed it!\n)
• return 0

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Sample 2 Dissection

• What more it has?
• Macro definition
• Variable declaration
• Operations represented by operators
• Conditional computation
• Input Processing
• Loops three chances

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Syntax Dissection

• What is syntax?
• How to put your C elements together into a
  program?
• Variable declaration,
• Identifier case, keywords, style
• datatype specification
• char, short, int, long, float, double
• Operators
• , -, , /, , , --, gt, lt, , , ,
• Priority and Precedence
• Associativity

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More

• Preprocessor directive
• macro
• header file inclusion
• Loop constructs
• for, while, do-while, break, continue, label--go
• Conditional statements
• If else, ifelse if, switch, break
• Function definition
• return type, parameter definition, parameter
  passing
• Standard library and function calls

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Walk through

• C program hello.c
• emacs, vi, vim, pico, joe
• Compilation hello.o, a binary file
• gcc -c hello.c
• Linking a.out or hello, an executable file
• gcc hello.o
• gcc -o hello hello.o
• Loading (dynamical linking) and execution
  ./hello
• ./a.out
• ./hello

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Take home practice

• Walk through sampe1 and sample2
• preprocessing, compilation, linking,
  loading/execute
• Modify and repeat once more if you can
• I will put the instructions on course webpage
  today.

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Recap of last lecture

• include ltstdio.hgt / Preprocessor directive
  /
• define MAGIC 10 / Macro substitution/
• int main(void) / Every C program has a main
  function/
• int i0 /
  Variable declaration/
• int factor, remainder
• while (i lt 3) /Control flow/
• printf(Guess a factor of MAGIC larger
  than 1 ") /input output/
• scanf("d, factor)
• remainder MAGIC factor
  /Operations represented by operators/
• if (remainder 0) /conditional
  statement/
• printf(You got it!\n)
• else
• printf(Sorry, You missed it!\n)
• return 0 /Return clause/

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Recap of last lecture

• Program environment Unix System
• stdsun.cse.ohio-state.edu
• gcc compiler
• Walk through your program
• http//www.cse.ohio-state.edu/lina/teaching/cse45
  9-21/instructions.html

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Types, Operators, and Expressions

• Constants
• Sample constants
• Variables
• Declaration must be declared before being used,
  declaration should be made before any execution
  statements.
• Naming
• Type
• specify the set of values a variable can have and
  what operations can be performed on it.
• basic types char, int, long, float, double, void
• other types arrary,pointer, enumeration,
  structure
• Type cast
• Initialization optional
• Operator
• Type conversion
• Precedence
• Associativity
• Operations What is to be done to the data
  objects
• Samples
• Expression
• Conditional expression

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Sample constants

• int 123, -1, 2147483647, 040 (octal), 0xab
  (hexadecimal)
• unsigned int 123u, 2107433648, 040U (octal), 0X02
  (hexadecimal)
• long 123L, 0x1FFFl (hexadecimal)
• unsigned long 123ul, 0777UL (octal)
• float 1.23F, 3.14e0f
• double 1.23, 2.718281828
• long double 1.23L, 9.99E-9L
• char 'A', 'B'
• character constant is an integer, can be used in
  numeric operations.
• Special characters \\ (backslash), \n (newline),
  \t (tab), \', \", ...
• How about \000,\xhh?
• How about \0?
• String constant( reference as pointers)
• x
• abcde
• Representation abcde\0

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Variable Declaration

• Declaration
• Purpose define a variable before it is used.
• Format type identifier , identifier
• How to Declare an array? A string?
• char line6
• char s
• Qualifier
• const
• const int a9 /Right/
• const in a
• a9 /compliers will give warning message/
• static

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Variable Naming

• Keywords are reserved words, and may not be used
  as identifiers
• auto, double, int
• a-z, A-Z, 0-9, and _
• The first character must be a letter or _
• Case sensitive
• Good naming style should
• Separate words with _' or capitalize the first
  character
• Use all UPPERCASE for symbolic constant, macro
  definitions, etc
• Be consistent
• Be meaningful

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How to use void?

• void a()
• Here a is a function name, void represents that
  this function has no return value.
• void a
• Here a is a pointer, void represents that this
  pointer can point to any data type.
• int a(void)
• Here a is a function name, void represents that
• the parameter lists checking can be omitted.

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Type Cast

• A type coercion (type) identifier
• Example
• int i 258
• char a / range -128 to 127 /
• a (char) i / What is the value of a? /
• i0x00000102
• a0x02

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Static Variable

• Program 1 Program2
• include ltstdio.hgt include ltstdio.hgt
• int increment() int increment()
• static int x 0 int x 0
• x x
• return x return x
• int main( ) int main()
• int y int y
• int i int i
• for (i0 ilt10i) for (i0 ilt10i)
• yincrement( )
  yincrement( )
• printf(d\n, y) printf(d\n, y)
• return 0 return 0

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Variable Initialization

• Initialization
• Each identifier can also be assigned
  (initialized) with a value of the same data type.
• char line6"ABCDE" ?/ copy ABCDE and /0 to
  array line /
• char line6ABCDEFG? /copy first 6 elements
  in string to array line /
• char s "ABCDE" / s point to a constant/
• Attention Direct assignment from a constant
  string can only happen at initialization but not
  assignment statement!
• Char line6
• Char s
• LineABCDE / Wrong/ ---do you know why?
• sABCDE / Wrong /-----do you know why?
• sABCDE /Right/ -----do you know why?
• Initialization rules
• Automatic variable each time the function or
  block is entered (garbage)
• Non-automatic variable only once before the
  program executes
• External and static variable0 by default
• 
  
  

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Type conversion

• When an operator has operands of different types,
  the only automatic conversion is to convert a
  narrower operand into a wider operand without
  losing information.
• long doublelt-others doublelt-others
  floatlt-others intlt-char, short longlt-others
• Assignments the value of the right side is
  converted to the type of the left
• Function call in absence of a function
  prototype, char, short-gtint, float-gtdouble
• What if you want to convert a string of numbers
  to an integer?
• Example1
• What if you want to convert an integer into a
  string of numbers?
• Example2

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Example 1

• includeltctype.hgt
• / atoi convert s to integer /
• int atoi(char s )
• int i, n
• n0
• for (i0sigt0silt9i) /
  isdigit(si) / n10n(si-0)
• return n

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Example 2

• / itoa convert n to character in s/
• void itoa(int n,char s )
• int i,sign
• if((signn)lt0)
• n-n
• i0
• do
• sin100
• while ((n/10)gt0)
• if (signlt0)
• si-
• si\0
• reverse(s)

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Precedence and Associtivity

• Precedence The order in which operators are
  applied in expressions.
• 9-6/2
• Associativity The order in which expressions
  involving operators of the same precedence are
  evaluated.
• 96-4
• Use parentheses to specify a different order of
  evaluation. It is recommended to use parentheses
  for clear and easy to read programs. But you
  still need to be prepared for the complexity in
  general.
• Short circuit evaluation
• and are evaluated from left to right. If at
  any point, the value of expression is determined,
  evaluation stops.
• Example (xgt0.0)(sqrt(x)gt5.0)
• A summary of precedence and associtivity
• http//www.cse.ohio-state.edu/lina/teaching/cse45
  9-21/operators.html
• Examples
• printf(d \td\n,n,power(2,n))
• aii

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Operations represented by operators

• A summary of operators
• http//www.cse.ohio-state.edu/lina/teaching/cse45
  9-21/operators.html
• Some notes
• C has no keywords as true or false. They are
  non-zero or zero values, usually 1 or 0.
• d cgt0clt9
• What is the value of d?
• OR', AND' , and NOT' differences between
  bitwise and logical operators.
• 0x1011 0x0010 ( 0x0010) cgt0clt9
• Note the difference between assignment and equal
  operators. Don't make the mistake of using ''
  when you meant ''!
• operator can not be applied to float or double.
• 53 (2) 5.03(wrong)
• / Truncation
• ! Converts a non-zero operand into 0
• If (! valid)? if (valid 0)
• 
  
  
  

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Operations represented by operators

• Be careful using floats with equality. Use
  inequalities whenever possible
• 4.0 can be stored in memory as 3.9999999 or
  4.0000001
• float a, b
• If(ab) ./ Wrong/
• Array indexing ij, here j can only be integer.
• Increment and Decrement operators
• can only be applied to variable (ij) is
  illegal
• can be prefix or postfix
• int n3, y
• yn
• y n
• Assignment operators
• int x3,
• int y1
• xy1 / xx(y1) not xxy1 /
• What is the value of x?
• Should be 6, not 4

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Division Truncation

• include ltstdio.hgt
• int main( )
• int fahr
• for (fahr0 fahrlt300 fahrfahr20)
• printf(3d 6.1f\n, fahr, 5(fahr-32.0)/9)
• return 0
• include ltstdio.hgt
• int main( )
• int fahr
• for (fahr0 fahrlt300 fahrfahr20)
• printf(3d 6.1f\n, fahr, 5/9(fahr-32.0))
• return 0
• 
  
  

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Some samples

• int a, b, c
• a 2, b 1
• c 1 a - -- b
• /c3 b0/
• c 1 a - b --
• /c3 b-1/
• c 1 a - b
• /c3 b0/
• c 1 a - b
• /c3 b1/
• c (1 a, b)
• /c1 b1/
• c 1 (a, b)
• /c2 b1/