C Data Types

1. C Data Types Chapter 7 And other material

2. Representation • long (or int on linux) • Two’s complement representation of value. • 4 bytes used. • (Where n = 32) #include limits.h INT_MIN INT_MAX [ -2147483648, 2147483647]

3. Representation (cont.) • float • 4 bytes used. • #include float.h On my machine, linux: FLT_MIN=0.000000 FLT_MAX=340282346638528859811704183484516925440.000000 On my laptop, Windows Xp Pro: FLT_MIN=0.000000 FLT_MAX=340282346638528860000000000000000000000.000000

4. Representation (cont.) • double • 8 bytes used. • #include float.h On my machine, linux: DBL_MIN=2.225074e-308 DBL_MAX=1.797693e+308 On my laptop, Windows Xp Pro: DBL_MIN=2.225074e-308 DBL_MAX=1.797693e+308

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 • 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?

7. 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

8. Numerical Inaccuracies What prints? int sum = 0; for(i=0; i<1000; i++) sum = sum + 1.55; printf("sum 1.55 1000 times = %f\n", sum);

9. Numerical Inaccuracies What prints? float sum = 0.0; for(i=0; i<1000; 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 • 1.1254e+12 • -4.0932e-18

11. 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!

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; <- legal • int flag = 0; <- 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 Sunday+1 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; <- 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!

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)(today+1);

19. Enumerated (cont.) • for(today=monday; • today <= 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 it’s called. • Let’s look at a simple example similar to the evaluate example in the text.

21. 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)); }

22. 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

23. 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

24. 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

25. 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.)

26. Simple version of fig 7.13 y (x1,y1) (x2,y2) y = f(x) (x3,y3) (x0,y0) (x4,y4) x x0=a 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.