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) [ , ] INT_MAXINT_MIN #include limits.h

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

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

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

Numerical Inaccuracies float sum = 0.0; for(i=0; i<1000; i++) sum = sum ; printf("sum times = %f\n", sum); What prints? sum times = ???

Floating Point Must contain a decimal point (0.0, 12.0, -0.01) Can use scientific notation e e-18

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 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 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 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 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)); }

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=ax1x2x3X4 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:

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

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

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.