Lect 5 P. 1

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C Programming Basics

• Lecture 5

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ENG H192 Course Web Page

• A web page which contains the course syllabus,
  updated lecture notes and other useful
  information may be found at
• http//feh.eng.ohio-state.edu
• A copy of Professor Dick Busicks flowchart
  spreadsheet is on the Web site

3
C Program Basics

• C vs. C
• C is a subset of C. All of features in C are
  contained in C
• C adds more libraries with functions for object
  oriented programming
• C also adds more keywords and some added
  features.

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Keywords in C and C

• Certain words have a special meaning to the C or
  C compiler. They are called reserved words or
  keywords. We should not try to use these words
  as names of variables or function names in a
  program.
• The keyword list for C contains 32 words (see
  text, pg. 44). C adds 30 more keywords (see
  text, pg. 563).

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Some Keywords in C and C
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Program Structure in C

• EACH complete C program is composed of
• Comment statements
• Pre-processor directives
• Declaration statements
• One or more functions
• Executable statements

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Program Structure in C

• EACH complete C program is composed of
• Comment statements
• Pre-processor directives
• Comment statements
• Declaration statements
• Comment statements
• One or more functions
• Comment statements
• Executable statements
• Comment statements

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Comment Statements

• Formal Comments
• / Comment .. /
• Used for detailed description of functions or
  operations (for our benefit, not compilers).
• Can take multiple lines in source file.
• Informal Comments (only in C, not C)
• // Comment .. Ends at the end of line
• Used for quick comments like
• int temp // temporary variable for storing
  // the input value

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Pre-Processor Directives

• include -- header files for library functions
• Example
• include ltstdio.hgt
• define -- define constants and
  macros Examples
• define e 2.7182818
• define pi 3.14159265359

Note Space
Note Spaces
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Declarations

• Declarations tell the compiler what variable
  names will be used and what type of data each can
  handle (store).
• Example declarations
• int a, b, c
• float r, p, q
• double x, y, z
• char m, n

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Data Types

• Integer variables int a, b
• Integer variables, like a or b, store only whole
  numbers like 3 or 7, not 3.33 or 7.65, and only
  up to certain maximum values.
• Floating point variables float c, d
• Floating point variables, like c or d, store
  rational numbers, like 3.14159, but only a
  limited number of digits of precision.

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Internal Storage Representation

• Definitions
• Binary digit -- or a "bit", is either a 0 or a 1
• Byte -- usually a collection of 8 bits together
• Word -- often a collection of 4 bytes together
• On the SGI Unix system
• an "int" data type takes up 4 bytes
• (on some systems, an "int" is only 2 bytes)
• a "float" data type takes up 4 bytes
• a "double" data type take up 8 bytes
• a "char" data type takes up 1 byte

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Programs Have One or More Functions

• Even the main program is a function.
• The body of each user-written function is
  enclosed in braces, (or curly brackets)
• The syntax of a function is
• ltfunction typegt function_name (arg. list)
• / beginning of
  function /
• / end of function
  /

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Executable Statements

• Simple
• Declaring variables
• int temp
• char a
• Assigning Values
• temp 5 temp is assigned the value of 5
• Complex, i.e., Calling Functions
• plotxy (x, y)
• Calculations
• x (5. / 2 6) 7

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Arithmetic Operators

• multiply add
• / divide - subtract
• remainder, where
• x 13 5 / x will be equal to 3 /
• An expression can be used almost anywhere a
  variable of the same type can be used.
• Ex. expressions num 3, a d - 5, ...

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Arithmetic Operators Order of Evaluation

• Parentheses () Evaluate from the inside out
• Multiplication, Division, and Remainder
• , /, and
• Addition and Subtraction
• and -
• NOTE Multiple occurrences of operations with
  the same precedence evaluate from left to right.
  (DD text, pg. 38)

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Arithmetic Operators Order of Evaluation

• For example
• x 2 3 - (4 5) 8 7
• x 2 3 - 9 8 7
• x 6 - 9 8 7
• x 6 - 9 1
• x -3 1
• x -2

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Arithmetic Operators Order of Evaluation

• Another example
• x 6 / 2 1 - 3 8 4

x 33
x 6 / (2 1) - (3 8) 4
x -42
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Mixed Mode Arithmetic

• When performing arithmetic operations, the "mode"
  will one of
• Floating point, if both operands are floating
  point
• Integer, if both operands are integer
• Mixed, if one operand in integer and the other is
  floating point -- the result is floating point
• Integer operations produce integer results
  (remember how you first learned to to division?)

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Assignment Operators

• Operator Example Meaning
• x 5 x 5
• x 5 x x 5
• x 5 x x 5
• / x / 5 x x / 5
• x 5 x x 5
• x 5 x x 5

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Assignment Operators

• Example of assignment operators
• int a 4, b 2, c 36
• a b / This adds b to a, a ? /
• c / a b / What is value of c
  now? /

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Assignment Operators

• Example of assignment operators
• int a 4, b 2, c 36
• a b / This adds b to a, a ? /
• Answer a a b, so a 4 2 or a 6
• c / a b / What is value of c now? /

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Assignment Operators

• Example of assignment operators
• int a 4, b 2, c 36
• a b / This adds b to a, a ? /
• Answer a a b, so a 4 2 or a 6
• c / a b / What is value of c now? /
• Answer c c / (a b), and a 6 now,
• so c 36 / (6 2), so c 36 / 8 or c
  4

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Increment/Decrement Operators

• Operator Meaning When?
• count count count 1 After use
• count count count 1 Before use
• count-- count count - 1 After use
• --count count count - 1 Before use

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Increment/Decrement Operators

• Examples of increment and decrement operators
• int a 4, b 2, c
• c a b--
• / What are the values of a, b, c now? /
• c b-- - a
• / What are the values of a, b, c now? /

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Increment/Decrement Operators

• Examples of increment and decrement operators
• int a 4, b 2, c
• c a b--
• / What are the values of a, b, c now? /
• (Answers a 5, b 1, c 7)
• c b-- - a
• / What are the values of a, b, c now? /

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Increment/Decrement Operators

• Examples of increment and decrement operators
• int a 4, b 2, c
• c a b--
• / What are the values of a, b, c now? /
• (Answers a 5, b 1, c 7)
• c b-- - a
• / What are the values of a, b, c now? /
• (Answers a 6, b 0, c -5)

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Relational Operators

• Operator Meaning
• lt Less Than
• gt Greater Than
• lt Less Than or Equal To
• gt Greater Than or Equal To
• Exactly Equal To
• ! Not Equal To

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Relational Operators

• Used for asking questions like
• Is x bigger than 10?
• In C, the value of 1 stands for true and 0 stands
  for false. But C will recognize any non zero
  value as true.
• NOTE "" is NOT same as ""

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Logical Operators

• ! (not)
• Ex a ! b is true if a and b are not equal
• (and)
• Ex 5lt6 7gt4 is true, but
• 5gt6 7gt4 is not true (i.e., false)
• (or)
• Ex 5gt6 7gt4 is true
• 5lt6 7lt4 is also true

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Exponentiation Operations

• Exponentiation is not written as x2 or x2
• C does not have an exponentiation operator. You
  can use the math function pow (a, b) which
  raises a to the b power. You must put a include
  ltmath.hgt in your source code and must also use
  the -lm switch in your compile command when on
  the SGI UNIX system.
•  
• Ex gtg -o myprog.out myprog.cpp

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Skeleton Program

• //
• / Name Brutus Buckeye /
• / Seat No. 0, Instr W. Hayes /
• / Program progname/assignment /
• //
• include ltstdio.hgt
• include ltstdlib.hgt
• include ltmath.hgt
• int main ( )
• statements

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Shell for programs

• Create a skelton.cpp file as a basis for your
  assignments
• Going to look much like Skeleton program on
  previous slide
• USAGE for an program
• Open skelton.cpp
• Save to name for program
• Edit program

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Todays Assignment

• Todays Assignment is G04
• G03 has a C program that calculates values and
  assigns them to variables.
• You are to do the calculations by hand (quiz and
  midterm material!!) and print the answers on the
  problem sheet.
• Then, copy the program into your account and run
  it to get the correct answers. Compare your hand
  calculations to the computers calculations.
• What needs to be added to the code so that you
  know what the computer calculated?