C Data Types

1
C Data Types

• Chapter 7
• And other material

2
Representation

• long (or int on linux)
• Twos complement representation of value.
• 4 bytes used.
• (Where n 32)

include limits.h
INT_MAX
INT_MIN
-2147483648, 2147483647
3
Representation (cont.)

• float
• 4 bytes used.
• include float.h
• On my machine, linux

FLT_MIN0.000000 FLT_MAX3402823466385288598117041
83484516925440.000000
On my laptop, Windows Xp Pro
FLT_MIN0.000000 FLT_MAX3402823466385288600000000
00000000000000.000000
4
Representation (cont.)

• double
• 8 bytes used.
• include float.h
• On my machine, linux

DBL_MIN2.225074e-308 DBL_MAX1.797693e308
On my laptop, Windows Xp Pro
DBL_MIN2.225074e-308 DBL_MAX1.797693e308
5
C Scalar Types

• Simple types
• char
• int
• float
• double
• Scalar, because only one value can be stored in a
  variable of each type.

6
Check Inside Your Program

• Dont depend on your assumptions for size.
• Use the internal variables INT_MAX, INT_MIN to
  verify what you believe to be true.
• Otherwise, youll overflow a variable.

i INT_MAX printf(d d\n, i, i1) //
What prints?
7
Check Inside Your Program

• Dont depend on your assumptions for size.
• Use the internal variables INT_MAX, INT_MIN to
  verify what you believe to be true.
• Otherwise, youll overflow a variable.

i INT_MAX printf(d d\n, i, i1) //
What prints?
2147483647 -2147483648
8
Numerical Inaccuracies
What prints?
int sum 0 for(i0 ilt1000 i) sum sum
1.55 printf("sum 1.55 1000 times f\n",
sum)
9
Numerical Inaccuracies
What prints?
float sum 0.0 for(i0 ilt1000 i) sum
sum 1.55 printf("sum 1.55 1000 times
f\n", sum)
sum 1.55 1000 times 1550.010864
???
10
Floating Point

• Must contain a decimal point (0.0, 12.0, -0.01)
• Can use scientific notation
• 1.1254e12
• -4.0932e-18

11
char data type

• One byte per character.
• Collating sequence
• a lt b lt c lt d lt
• A lt B lt C lt D lt
• 0 lt 1 lt 2 lt 3 lt
• But a lt A or A lt a ??? Not for sure!

12
User Defined Types (typedef)

• This is how you can expand the types available to
  a particular program.
• typedef type-declaration
• E.g. typedef int count
• Defines a new type named count that is the same
  as int.
• count flag 0 lt- legal
• int flag 0 lt- same as

13
User Defined Types (typedef)

• Many more uses (later)

14
Enumerated Types

• In the old days, we would make an assignment like
  1 means Monday, 2 means Tuesday, 3 means
  Wednesday
• But this way, you could have Sunday1 and this
  would be meaningless.
• A better way is using enumerated types.

15
Enumerated Types (cont.)

• Example

typedef enum monday, tuesday, wednesday,
thursday, friday, saturday, sunday
DayOfWeek_t

• Some default identification for user defined
  types
• _t
• Explicitly specify the values!

16
Enumerated (cont.)

• Now, you can define a new variable
• DayOfWeek_t WeekDays
• WeekDays monday lt- legal
• WeekDays 12 lt- illegal
• WeekDays someday lt- illegal
• Now, internally, the computer associates 0,1,2,
  with monday, tuesday, But you dont have to
  worry!

17
Enumerated rules

• Enumerated constants must be identifiers, NOT
  numeric (1,3,-4), character (s, t, p), or
  string (This is a string) literals.
• An identifier cannot appear in more than one
  enumerated type definition.
• Relational, assignment, and even arithmetic
  operators can be used.

18
Enumerated (cont.)

• if(today saturday)
• tomorrow sunday
• else
• tomorrow (DayOfWeek_t)(today1)

19
Enumerated (cont.)

• for(todaymonday
• today lt friday
• today)

20
Passing a Function Name as a Parameter

• In C it is possible to pass a function name as a
  parameter.
• Gives the called function the ability to do
  something using different functions each time
  its called.
• Lets look at a simple example similar to the
  evaluate example in the text.

21
E.G. Passing a function
include ltstdio.hgt include ltmath.hgt double
evaluate(double f( ), double) int main (void)
double sqrtvalue, sinvalue
sqrtvalue evaluate(sqrt, 12.5)
printf("f \n", sqrtvalue) sinvalue
evaluate(sin, 0.5) printf("f \n",
sinvalue) double evaluate ( double f(double
f_arg), double pt1) return
(f(pt1))
22
E.G. Passing a function
include ltstdio.hgt include ltmath.hgt double
evaluate(double f( ), double) int main (void)
double sqrtvalue, sinvalue
sqrtvalue evaluate(sqrt, 12.5)
printf("f \n", sqrtvalue) sinvalue
evaluate(sin, 0.5) printf("f \n",
sinvalue) double evaluate ( double f(double
f_arg), double pt1) return
(f(pt1))
3.535534 0.479426
23
E.G. Passing a function
include ltstdio.hgt include ltmath.hgt double
evaluate(double f( ), double) int main (void)
double sqrtvalue, sinvalue
sqrtvalue evaluate(sqrt, 12.5)
printf("f \n", sqrtvalue) sinvalue
evaluate(sin, 0.5) printf("f \n",
sinvalue) double evaluate ( double f(double
f_arg), double pt1) return
(f(pt1))
3.535534 0.479426
24
E.G. Passing a function
include ltstdio.hgt include ltmath.hgt double
evaluate(double f( ), double) int main (void)
double sqrtvalue, sinvalue
sqrtvalue evaluate(sqrt, 12.5)
printf("f \n", sqrtvalue) sinvalue
evaluate(sin, 0.5) printf("f \n",
sinvalue) double evaluate ( double f(double
f_arg), double pt1) return
(f(pt1))
3.535534 0.479426
25
Lab 6 Trapezoidal Rule

• Write a program to solve for the area under a
  curve y f(x) between the lines xa and xb.
  (See figure 7.13 on page 364.
• Approximate this area by summing trapezoids
  (Formed by a line from x0 vertical up to the
  function, to f(x0), then straight line to f(x1),
  back down to the x-axis, and left to original.)

26
Simple version of fig 7.13
y
(x1,y1)
(x2,y2)
y f(x)
(x3,y3)
(x0,y0)
(x4,y4)
x
x0a
x1
x2
x3
X4 n 4
27
Lab 6 assumptions

• Function is positive over the interval a,b.
• (for n subintervals of length h) h(b-a)/n
  Trapezoidal rule is

28
Lab 6 (cont.)

• Write a function trap with input parameters a,b,n
  and f that implements the trapezoidal rule.
• Call trap with values for n of 2,4,8,16,32,64,
  and 128 on functions

29
Lab 6 (cont.)

• Function h defines a half-circle of radius 2.
  Compare your approximation to the actual area of
  this half-circle.
• Note the trapezoidal rule approximates

30
Exam 1 On Wednesday

• Closed Book!
• One 8-1/2x11 paper, both sides allowed.
• Sit with a space on either side of you.
• Only 4 function calculators allowed.
• Chapters 1-6.
• Linux.
• Makefiles.
• Introduction to Pointers.