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Binary Numbers

* Quick look at Binary Numbers
        * Let's look at the decimal system first
        * consider 5281
        * The "1" is in the 1's column
        * The "8" is in the 10's column
        * The "2" is in the 100's column
        * The "5" is in the 1000's column
        * One column for each power of 10
    * So we have: 5 * 1000 + 2 * 100 + 8 * 10 + 1 * 1
    * Now let's move to the binary number system.
    * Consider this number: 110101
      Starting at the right, we have:
        * a 1 in the 1's column
        * a 0 in the 2's column
        * a 1 in the 4's column
        * a 0 in the 8's column
        * a 1 in the 16's column
        * a 1 in the 32's column
        * Note: there is a separate column for each power of 2.
      So we have: 1*32 + 1*16 + 0*8 + 1*4 + 0*2 + 1 = 53
 
    * Try a few more:
 
        * 1 1 1 1   = 1*8 + 1*4 +1*2 +1*1 = 15
        * 0 1 0 1   = 0*8 + 1*4 + 0*2 + 1*1 = 5
        * 1 0 1 1 1 = 1*16 + 0*8 + 1*4 + 1*2 + 1*1 = 23
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Library Functions

  * Library Functions - Some functions are so useful
    that they have become standardized, and are available
    to every C programmer. These are called library
    functions.

  * There are actually several different libraries:

    * The "Standard Library"
    * Specialized Libraries:
      ex:
        * jpeg libraries
        * pdf libraries
        * mp3 libraries

  * We'll only cover functions from the standard library
    in this class.

  * Example: the absolute value function

    #include<stdio.h>
    #include<stdlib.h>

    int main(void)
    {
        int x, y, z;

        x = -5;
        y = 10;
        z = abs(x) + 1;
        printf("%d %d %d\n", x, y, z);
        printf("%d\n", abs(x) );
        printf("%d\n", abs(3 - 6) );
        printf(%d\n", abs(z - y) );
        printf(%d\n", abs(y - (x - z) );
        printf(%d\n", abs(x - abs(x) );
    }

    * Output of the above program:
        -5 10 6
        5
        3
        4
       21
       10

    * Explanation of the "#include <stdlib.h>" line at the top
      of the program:
        * Each standard library function is associated
           with a "standard header file"; 
        * abs is associated with "stdlib.h"
        * The "#include" directive tells the compiler to
          get "stdlib.h" (it knows where to look) and insert it into 
          the top of your program.
        * (Note: The brackets tell the compiler to look in
           the "/usr/include" directory for the stdlib.h file.)

    * The prototype for abs:

            int abs (int j);

      Tells you all you need to know about abs:
        * It has one parameter (an integer), and so
          the argument (constant, variable, or expression) 
          should be an integer; 
        * The return value is an integer.

    * Try this:
        % man abs 

      All the standard library functions have "man pages", just 
      like the shell commands.

    * another standard library function: pow

        * prototype:  double pow(double x, double y);

          indicates:
            * 2 "double" parameters (thus 2 double arguments
              are needed in a call to pow)
            * return type is double

        * returns the value of x raised to the power of y.

        * requires: math.h

          #include<math.h>    <--- put this at top of your program

        * example:

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

          int main (void)
          {
            double x,y, z;

            x = 2.0;
            y = 10.10;
            z = pow(x,y);
            printf("z's value is:  %.2f\n", z);
          }

    * A special note about math.h:

      If you need to include math.h, then you also need to
      do one more thing. When you compile, you have to
      use the "-lm" option. 

      Example:
          * Assume your C program file name is pyth.c
          * Here's how to compile:
                % gcc -Wall -o pyth pyth.c -lm
          * Here's what "-lm" means:
              * -l means *link*
              * the "m" instructs the compiler to get a file
                called "libm.a" (it knows which directory
                to find this in.)
              * basic idea: link your program together 
                with a file containing pre-compiled code
                for math operations.

    * the sqrt function:

      example:

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

          int main (void)
          {
            double x,y, z;

            x = 16.0;
            y = sqrt(x);
            printf("y's value is:  %.2f\n", y);
          }


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The Switch Statement

Example:

    switch (grade) {
        case 'A': 
            printf("Excellent");
            break;
        case 'B': 
            printf("Good");
            break;
        case 'C': 
            printf("Not bad");
            break;
        case 'D','F': 
            printf("Sorry");
            break;
        default: 
            printf("Incorrect grade value");
    }

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