C Data Types

Chapter 7 And other material

Representation long (or int on

linux) Two’s complement

representation of value.

4 bytes used. (Where n = 32)

122 11 nton

[ -2147483648, 2147483647]

INT_MAXINT_MIN

#include limits.h

Representation (cont.) float

4 bytes used. #include float.hOn my machine, linux:

FLT_MIN=0.000000FLT_MAX=340282346638528859811704183484516925440.000000

On my laptop, Windows Xp Pro:

FLT_MIN=0.000000FLT_MAX=340282346638528860000000000000000000000.000000

Representation (cont.) double

8 bytes used. #include float.hOn my machine, linux:

DBL_MIN=2.225074e-308DBL_MAX=1.797693e+308

On my laptop, Windows Xp Pro:

DBL_MIN=2.225074e-308DBL_MAX=1.797693e+308

C Scalar Types

Simple types char int float double

Scalar, because only one value can be stored in a variable of each type.

Check Inside Your Program

Don’t depend on your assumptions for size.

Use the internal variables INT_MAX, INT_MIN to verify what you believe to be true.

Otherwise, you’ll overflow a variable.i = INT_MAX;

printf(“%d %d\n”, i, i+1); // What prints?

Check Inside Your Program

Don’t depend on your assumptions for size.

Use the internal variables INT_MAX, INT_MIN to verify what you believe to be true.

Otherwise, you’ll overflow a variable.i = INT_MAX;

printf(“%d %d\n”, i, i+1); // What prints?

2147483647 -2147483648

Numerical Inaccuracies

int sum = 0;

for(i=0; i<1000; i++) sum = sum + 1.55; printf("sum 1.55 1000 times = %f\n", sum);

What prints?

Numerical Inaccuracies

float sum = 0.0;

for(i=0; i<1000; i++) sum = sum + 1.55; printf("sum 1.55 1000 times = %f\n", sum);

What prints?

sum 1.55 1000 times = 1550.010864

???

Floating Point Must contain a

decimal point (0.0, 12.0, -0.01)

Can use scientific notation 1.1254e+12 -4.0932e-18

12101254.1 x18100932.4 x

char data type

One byte per character. Collating sequence

‘a’ < ‘b’ < ‘c’ < ‘d’ < … ‘A’ < ‘B’ < ‘C’ < ‘D’ < … ‘0’ < ‘1’ < ‘2’ < ‘3’ < … But ‘a’ < ‘A’ or ‘A’ < ‘a’ ??? Not for

sure!

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; <- legal int flag = 0; <- same as

User Defined Types (typedef)

Many more uses (later)

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 Sunday+1 and this would be meaningless.

A better way is using enumerated types.

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!

Enumerated (cont.) Now, you can define a new variable DayOfWeek_t WeekDays; WeekDays = monday; <- legal WeekDays = 12; <- illegal WeekDays = someday; <- illegal Now, internally, the computer

associates 0,1,2,… with monday, tuesday,… But you don’t have to worry!

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.

Enumerated (cont.)

if(today == saturday) tomorrow = sunday; else tomorrow = (DayOfWeek_t)

(today+1);

Enumerated (cont.)

for(today=monday; today <= friday; ++today) { … }

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 it’s called.

Let’s look at a simple example similar to the evaluate example in the text.

E.G. Passing a function

#include <stdio.h>#include <math.h>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));}

E.G. Passing a function

#include <stdio.h>#include <math.h>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

E.G. Passing a function

#include <stdio.h>#include <math.h>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

E.G. Passing a function

#include <stdio.h>#include <math.h>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

Lab #6 : Trapezoidal Rule

Write a program to solve for the area under a curve y = f(x) between the lines x=a and x=b. (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.)

Simple version of fig 7.13

y

x

(x0,y0)

(x1,y1)

(x2,y2) (x3,y3

)

(x4,y4)

y = f(x)

x0=a x1 x2 x3 X4

n = 4

Lab #6 : assumptions Function is

positive over the interval [a,b].

(for n subintervals of length h) h=(b-a)/n Trapezoidal rule is: ))(2)()((

2

1

1

n

iixfbfaf

hT

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

)14159.3,0(

)sin()( 2

bafor

xxxg

)2,2(

4)( 2

bafor

xxh

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

b

a

dxxf )(

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.