Functions

1
Functions

• ONLY functions in C
• C programs are a collection of functions. All C
  programs have at least one function - main()
• main() can then call other functions such as
  printf()
• functions take arguments
• e.g... printf(hello) - hello is the argument
• You can write your own functions with/without
  arguments
• A function without return value is called a
  procedure in Pascal, or a subroutine in Fortran

2
Reserved Words
3
Variables and Data types

• Local variables
• those for use within a function only
• declared at the beginning of a function
• Global variables
• those for use in all functions
• declared in main block (outside the other
  function bodies) and available for all functions
• 4 base data types
• char
• int (can be short, long, signed, unsigned)
• float
• double (is long float can be long double)

4
Input/Output

• input - scanf()
• output - printf()
• Need for format specifiers
• indicate the data type
• String - s
• character c
• int d (ld for long int), (or i, li)
• float f (lf for double), (or exponential form
  e, E(2.3e02, 2.3E02), general form g,
  G(automatically select f or E)
• e.g.. printf(Student grade is f,sgrade)
• where sgrade is of type float
• e.g.. scanf(d,noofstudents)
• where noofstudents is of type int
• where means address of

5
More about printf()

• takes a string as an argument
• special notation for hard to get characters
• \n for new line
• \t for tab
• \r for carriage return
• \b for backspace
• \\ for backslash
• \ for quotes
• \f for form feed
• integer printing -145
• I -gt-145 6d -gt bb-145 -6d -gt-145bb
• float printing 157.8926
• f -gt157.892600 6.2 -gt157.89e -gt1.57826e02
  .1E-gt1.5E02

6
More about scanf()

• Complements printf()
• Same format specifiers
• Need to use the address of operator,
• Without the address of operator you may crash
  the system
• scanf(d,noofstudents)
• scanf(d, year)
• printf(Enter the distance and velocity\n)
• scanf(lf lf, distance, velocity)
• Enter the distance and velocity
• 10 15.5

7
Operators

• Assignment x y z
• Relational lt, lt, gt, gt, , !, e.g. if (x y)
• Arithmetic - ,-,/,,
• Types must be correct for expressions
• Expressions can be mixed in some cases
• e.g.. int and float
• Generally, the expression if mixed is converted
  to the type of highest accuracy
• You can enforce the type with the cast operator
• e.g. Celsius (int) (Fahrht - 32) 5 / 9)
• This forces the answer to be an integer
• Logical !, ,

8
Expressions

• More or less as in Pascal except
• Use instead of for assignment
• The is part of the statement
• Increment operator
• j i 1 can be written j i
• j takes the value of i then add 1
• OR j i
• j takes the value of i incremented by 1
• Decrement operator
• j i - 1 can be written j i--
• OR j --i

9
Expressions

• and -- can be used in expressions
• If used in a prefix position, the identifier is
  modified, and then the new value is used in
  evaluating the rest of the expression
• if used in a postfix position, the old value is
  used to evaluate the rest of the expression, and
  then the identifier is modified
• Example
• Let x2, y4, before each statement executed.
  Find the results!
• zxy x y z
• zxy x y z
• xy x y
• yx x y