4.5 Bitwise Operators

1

• 4.5 Bitwise Operators
• AND
• Inclusive OR
• Exclusive OR
• Right Shift
• Ones Complement (unary)
• Examples

2

• 4.6 Basic File I/O
• Essentials of a file
• Example
• - read data from a file data_in
• - write data to a file data_out
• include
• include
• main()
• float var1, var2
• int var3
• double var4
• FILE f1, f2
• f1 fopen ("data_in", "r")
• f2 fopen ("data_out", "w")
• fscanf (f1, "f, f", var1, var2)

3
file data_in 123.4, 2.3456 10,
0.234567 file data_out sum var1 var2
125.7456 var3 10 var4 0.234567

• In general, fpfopen(name, mode)
• mode can be r, w, a
• (a means append)
• Opening an existing file with w causes the old
  data to be discarded
• With a, the old data is still there
• Trying to read a non-exist file is an error

4

• 4.7 The Increment and Decrement operators , --
• k or k means k k1
• k-- or --k means k k-1
• Example 1a
• int k1
• k
• Result k is now equal to 2
• Example 1b
• int k1
• k
• Result k is now equal to 2

5

• Example 2a
• int k4
• k--
• Result k is now equal to 3
• Example 2b
• int k4
• --k
• Result k is now equal to 3

6

• 4.8 Difference between k and k
• Example 1
• k1
• i10(k) / After the operation, i is 10 /
• jk / now j is 2 /
• k is incremented after the expression is
  evaluated
• i.e.
• i10(k) means
• i10k kk1

7

• Example 2
• k1
• i10(k) / After the operation, i is 20 /
• jk / now j is 2 /
• k is incremented before the expression is
  evaluated
• i.e.
• i10(k) means
• kk1 i10k
• 4.9 Difference between k- - and - -k
• Similar to

8

• 4.10 The while Loop
• General Format
• while(expression)
• statements ...
• Flow chart
• Example 1
• float x 0.0, sum 0.0
• while(x0)
• sum sum x
• scanf(f,x)
• printf(5.2f\n, sum)
• Input
• 1.0
• 0.5
• 1.0

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Example 2 float x 0.0, sum 0.0
while(x0) scanf(f,x) sum
sum x printf(5.2f\n,
sum) Input 1.0 0.5
1.0 -1.0 Output 1.5
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• 4.11 The do-while Loop
• General Format
• do
• statements ...
• while(expression)
• Flow chart

11

• Example 1 int k, count 0
• do scanf(d,k)
• if( k2 ) count
• while (k)
• printf(d\n,count)
• Input Output
• 1 4
• 2
• 3
• 2
• 2
• 4
• 2
• 0

12

• 4.12 The break Statement
• When the break statement is encountered within a
  loop, the loop is terminated immediately.
• Example
• sum 0
• for(k0 k
• scanf(d,i)
• if(i10) break
• sum sum i
• printf(d\n,sum)
• Input Output
• 1 6
• 2
• 3
• 15

13

• 4.13 The continue Statement
• Do the next iteration, skipping the remaining
  statements.
• Example
• sum 0
• for(k0 k
• scanf(d,i)
• if(i10) continue
• sumsumi
• printf(d\n,sum)
• Input Output
• 1 11
• 2
• 3
• 15
• 5

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4.14 Nested loops - Example / SYEN 4385 Example
program to illustrate nested loops. This
program evaluates numerically the derivative of
log(x) for x1,2,...,10 using central difference
scheme with h1/2,1/4,1/8,1/16, .... /
15
include include main()
int i, j float x, dfdx, h i 1
while(ix1.0i printf("5.1f ",x)
for(j1jevaluate derivative / dfdx
(log(xh)-log(x-h))/(2h) printf("13.3e
",dfdx) i printf("\n")
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Nested loops - example OUTPUT 1.0
1.099e00 1.022e00 1.005e00 1.001e00 2.0
5.108e-01 5.026e-01 5.007e-01 5.002e-01 3.0
3.365e-01 3.341e-01 3.335e-01 3.334e-01 4.0
2.513e-01 2.503e-01 2.501e-01 2.500e-01 5.0
2.007e-01 2.002e-01 2.000e-01 2.000e-01 6.0
1.671e-01 1.668e-01 1.667e-01 1.667e-01 7.0
1.431e-01 1.429e-01 1.429e-01 1.429e-01 8.0
1.252e-01 1.250e-01 1.250e-01 1.250e-01 9.0
1.112e-01 1.111e-01 1.111e-01 1.111e-01 10.0
1.001e-01 1.000e-01 1.000e-01 1.000e-01
17

• 4.15 The switch Statement
• General Format
• switch(variable)
• case constant_1
• statements
• break
• case constant_2
• statements
• break
• case constant_N
• statements
• break
• default
• statements

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• The switch statement is used to select one of
  several alternative paths in program execution,
  based on the value of a single variable.
• If the variable matches constant i (which can
  be int or char type), the statements between
  constant i and break will be executed
  otherwise, the default statements are executed.
  

19

• 5 Data Types
• Five basic data types
• int, float, double, char, void
• Type modifiers
• signed, unsigned
• short, long
• How many combinations? 36?
• ANSI standard see page 109, Teach Yourself C
  (3rd.), Herbert Schildt
• HP machine implementation see Table 1 in page
  5, your Notes
• Also, look at files limits.h and float.h
  under directory /usr/include

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• 5-1 int
• At least 16 bits
• Machine dependent
• HP machine 32 bits
• signed
• int i
• signed i
• signed int i
• unsigned
• unsigned i
• unsigned int i

21

• To print printf(u, i)
• To read scanf(u, i)

• long
• long int k
• long k
• The variable in some other systems has twice the
  byte length as int, but in our HP system long is
  same as int
• unsigned long int k is same as unsigned int k

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• short
• short int k
• short k
• The variable has half the byte length as int
• HP size 2 bytes
• To print printf(d, k)
• To read scanf(d, k)

23

• unsigned short
• unsigned short int k
• unsigned short k
• HP size 2 bytes
• To print printf(u, k)
• To read scanf(u, k)

24

• 5-2 float
• HP machine 32 bits
• float x

• To print
• printf(f, x)
• printf(e, x)
• printf(g,x)
• To read
• scanf(f, x)
• scanf(e, x)
• scanf(g, x)
• If g is used, the computer will choose f or e
  automatically, depending on which results in the
  most compact output

25

• 5-3 double
• HP machine 64 bits
• double x

• To print
• printf(lf, x)
• printf(le, x)
• printf(lg,x)
• To read
• scanf(lf, x)
• scanf(le, x)
• scanf(lg, x)

26

• 5-4 char
• HP machine 8 bits
• char s

• To print
• printf(c,s)
• To read
• scanf(c, s)

27

• 5-5 Type Casting
• C allows coercion that is forcing one variable
  of one type to be another type
• Examples
• int i float a 1.3
• i(int)a / i is now 1 /
• int i3 float a
• a(float)i / a is now 3.0 /
• int i char ch'A'
• i(char)ch / i is now 65 - ASCII code for A /

28

• 6 Functions
• You have already seen some C library functions
  such as exp, pow, ....
• You can also define your own functions
• 6-1 General Format
• return_type function_name
• (parameter1_type parameter1, parmater2_type
  parameter2, ...)
• statements
• return(expression)

29

• return_type double, float, int, char, ...
• return (expression)
• terminates execution of the function and
  returns control to the calling function
• evaluates the expression in ( ), and returns the
  value of the expression to the calling function
• Examples
• return (a)
• return (ab)
• return (5)
• You can call any function from main()
• You can call any function from another function
• You cannot call main() from other function

30

• 6-2 An example
• include
• float find_average(float, float) / prototype
  /
• main()
• float x5, y15, result
• / x, y are arguments /
• result find_average(x, y)
• printf("averagef\n", result)
• / a, b are parameters, i.e. formal arguments /
• float find_average(float a, float b)
• float average
• average(ab)/2
• return(average)

31

• 6-3 Usage of Type void
• If you do not want to return a value you can use
  the void function (note no return statement is
  requited in this case).
• Example to print out 1, 4, 9, 16, ...
• include
• void squares()
• main()
• squares
• / try to use squares() here to see what will
  happen /
• void squares()
• int loop
• for (loop1 loop
• printf("d\n", looploop)

32

• 6-4 Some Features of C
• 6-4-1 Arithmetic Operator
• Used for int only
• Produces the remainder when x is divided by y
• Recall Integer division truncates any
  fractional part

33

• 6-4-2 Conditional Expression
• if(ab)
• za
• else
• zb
• An equivalent and more efficient way to write
  this is
• z(ab)? ab
• Here ? is a ternary operator
• expression1 ? expression 2 expression3
• means if expression1 is true, then do
  expression2 otherwise do expression3

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6-4-3 Assignment Operators

• Equivalent statements
• x x 0.5 x 0.5
• x x - dx x - dx
• x x 10.0 x 10.0
• x x/100 x / 100
• In general
• expr1 op expr2 means
• expr1 (expr1) op (expr2)
• Other examples of op are

35

• 6-5 Global Variables
• Be declared outside of all functions (including
  main())
• Be visible to all functions that follows the
  declaration
• Values can be changed by these functions

36

• Example
• include
• void fn1()
• void fn2()
• int i float x
• main()
• i1 x10.0
• printf(d, f\n, i, x)
• fn1()
• printf(d, f\n,i,x)
• fn2()
• printf(d, f\n,i,x)
• void fn1()i x5
• void fn2()i10 xx

37

• 6-6 Local Variables
• Be declared inside a function
• Be visible only to the function in which they
  are declared
• Content of a local variable can only be changed
  by the corresponding function
• Be created upon entry into the function and
  destroyed upon exit

38

• Example
• include
• void fn1()
• main()
• int i float x
• i1 x10.0
• printf(main1 d, f\n,i,x)
• fn1()
• printf(main2 d, f\n,i,x)
• void fn1()
• int i float x
• i2 x15.0
• printf(fn1 d, f\n,i,x)
• OUTPUT
• main11, 10.000000

39

• 6-7 Static Variables
• Be local to a particular function
• Only initialized once during the first call to
  the function
• The value of a static variable on leaving the
  function remains intact
• On the next call to the function, the static
  variable still has the same value as the last
  time.

40

• Example
• include
• void stat()
• main()
• int i
• for(i0 i
• void stat()
• int nonstat_var0
• static int stat_var0
• printf("nonstaticd, staticd\n",
• nonstat_var, stat_var)
• nonstat_var
• stat_var
• OUTPUT