Tuesday 28 July 2015

Examples Using Arrays (Arrays Part three)

Now that we have gotten a grip over the basics of arrays ( part one and part two ), we will discuss some basic code examples involving arrays.

Strings:

Strings can be considered as arrays of characters;
     All strings end with null ('\0')
     Examples
        char string1[] = "hello";
       Null character implicitly added
       string1 has 6 elements
        char string1[] = { 'h', 'e', 'l', 'l',    'o', '\0’ };
     Subscripting is the same
string1[ 0 ] is 'h'
string1[ 2 ] is 'l'
      Input from keyboard
  char string2[ 10 ];
  cin >> string2;
     Puts user input in string
        Stops at first whitespace character
        Adds null character
     If too much text is entered then the data is written beyond array
      Printing strings
     cout << string2 << endl;
        Does not work for other array types
     Characters printed until null found

 This is shown in the examples below:


Static Arrays:

Recall static storage
–If static, local variables save values between function calls
–Visible only in function body
–Can declare local arrays to be static
•Initialized to zero
static int array[3];
If not static
–Created (and destroyed) in every function call



             

Sorting data using Arrays:

 Before getting into this example we should first know what Sorting data is, it is:
     An important computing application
     Virtually every organization must sort some data
        Massive amounts must be sorted
      Bubble sort
     Several passes through the array
     Successive pairs of elements are compared
        If increasing order (or identical), no change
        If decreasing order, elements exchanged
     Repeat these steps for every element
• Example:
        Go left to right, and exchange elements as necessary
          One pass for each element
        Original:   3  4  2  7  6
        Pass 1:      3  2  4  6  7   (elements exchanged)
        Pass 2:      2  3  4  6  7
        Pass 3:      2  3  4  6  7   (no changes needed)
        Pass 4:      2  3  4  6  7
        Small elements "bubble" to the top (like 2 in this example)
          Swapping variables
int x = 3, y = 4;
y = x;
x = y;
          What happened?
        Both x and y are 3!
        Need a temporary variable
          Solution
int x = 3, y = 4, temp = 0;
temp = x;  // temp gets 3
x = y;     // x gets 4
y = temp;  // y gets 3

              
              
             

Computing Mean, Mode and Median using Arrays:

First lets just look at what mean , median and mode actually are:
•Mean
–Average (sum/number of elements)
•Median
–Number in middle of sorted list
–1, 2, 3, 4, 5  (3 is median)
–If even number of elements, take average of middle two
•Mode
–Number that occurs most often
–1, 1, 1, 2, 3, 3, 4, 5 (1 is mode)
Now lets look at how we'll compute these.
               
                           











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