DECLARING ARRAYS


To reserve 12 elements for integer array c, the declaration needed is:
int c[ 12 ];


Likewise,
int b[ 100 ], x[ 25 ];
reserves 100 elements for the integer array b and 25 elements for the integer array x


Example


//Initializing an array
#include <iostream.h>
#include <iomanip.h>

int main()
{
   int i, n[ 10 ];

   for ( i = 0; i < 10; i++ )
	n[ i ] = 0;
   //This initializes the array.
   cout << "Element" << setw( 13 )
        << "Value" << endl;

   for ( i = 0; i < 10; i++ )
      cout << setw( 7 ) << i
	   << setw( 13 ) << n[ i ] << endl;
return 0;
}

If there are fewer initializers than elements in the array, the remaining elements are automatically initialized to zero.


Example
int n[ 10 ] = { 0 };
explicitly initializes the first element to zero and implicitly initializes the remaining nine elements to zero because there are fewer initializers than elements in the array.


Example


 
//Histogram printing program

#include <iostream.h>
#include <iomanip.h>

int main()
{
   const int arraySize = 10;
   int n[ arraySize ] = {19,3,15,7,11,9,13,5,17,1};

   cout << "Element" << setw( 13 ) << "Value"
	<< setw( 17 ) << "Histogram" << endl;

	for ( int i =1; i < arraySize; i++ ) {
	   cout << setw( 7 ) << i << setw( 13 )
		<< n[ i ] << setw( 9 );

	   for ( int j = 0; j < n[ i ]; j++ )
		cout << '*';
	   cout << endl;
	}

	return 0;
} 

PASSING ARRAYS TO FUNCTIONS


To pass an array argument to a function, specify the name of the array without any brackets.
For example, if array hourlyTemperatures has been declared as
int hourlyTemperatures[ 24 ];
the function call statement
modifyArray( hourlyTemperatures, 24 );
passes array hourlyTemperatures
and its size to function modifyArray


Example


The following program first prints the five elements of integer array a. Next, a and its size are passed to function modifyArray where each of a's elements is multiplied by 2. Then a is reprinted in main.


Next, the program prints the value of a[3] and passes it to function modifyElement which mulitplies its argument by 2 and prints the new value. Note that when a[3] is reprinted in main, it has not been modified because individual array elements are passed call-by-value.


Example


// Passing arrays and individual array
// elements to functions

#inlcude <iostream.h>
#include <iomanip.h>

void modifyArray( int [], int );
void modifyElement( int );

int main()
{
   const int arraySize = 5;
   int i, a[ arraySize ] = { 0, 1, 2, 3, 4 };

   cout << "Effects of passing entire array
            call by reference:"
        << "\n\nThe values of the original
           array are:\n";

   for ( i = 0; i < arraySize; i++ )
       cout << setw( 3 ) << a[ i ];

   cout << endl;

   // array a passed call-by-reference
   modifyArray( a, arraySize );

   cout << "The values of the modified array are:\n";

   for ( i = 0; i < arraySize; i++ )
     cout << setw( 3 ) << a[ i ];

   cout << "\n\n\n"
        << "Effects of passing array element 
            call-by-value:"
        << "\n\nThe value of a[3] is "
        << a[3] << '\n';

   modifyElement( a[ 3 ] );

   cout << "The value of a[3] is " 
        << a[3] ,, endl;

   return 0;
}

   void modifyArray( int b[], int sizeOfArray )
{
   for ( int j = 0; j < sizeOfArray; j++ )
       b[ j ] *= 2;
}

   void modifyElement( int e )
{
   cout << "Value in modifyElement is "
	<< ( e *= 2 ) << endl; 
}

SORTING ARRAYS


Sorting data is one of the most important computing applications.


The following program sorts the values of the ten element array a into ascending order. The technique we use is called BUBBLE SORT or the SINKING SORT because the smaller values gradually "bubble" their way upward to the top of the array like air bubbles rising in water, while the large values sink to the bottom of the array. The technique is to make several passes through the array. One each pass, successive pairs of elements are compared. If a pair is in increasing order or the values are identical we leave the values as they are. If a pair is in decreasing order, their values are swapped in the array.


Example


//This program sorts an array's values into
//ascending order.

#include <iostream.h>
#include <iomanip.h>

int main()
{
   const int arraySize = 10;
   int a[ arraySize ] = {2,6,4,8,10,12,89,68,45,37};
   int i, hold;

   cout << "Data items in original order\n";

   for ( i = 0; i < arraySize; i++ )
    cout << setw( 4 ) << a[ i ];

   for ( int pass = 0; pass < arraySize - 1; pass++ )

    for ( i = 0; i < arraySize - 1; i++ ) //one pass

     if ( a[ i ] > a[ i + 1 ] ) { // one comparison
        hold = a[ i ];            // one swap
        a[ i ] = a[ i + 1 ];
        a[ i + 1 ] = hold;
     }

   cout << "\nData items in ascending order\n";

   for ( i = 0; i < arraySize; i++ )
    cout << setw( 4 ) << a[ i ];

   cout << endl;
   return 0;
}

First the program compares a[ 0 ] to a[ 1 ], then a[ 1 ] to a[ 2 ], then a[ 2 ] to a[ 3 ], and so on until it completes the pass by comparing a[ 8 ] to a[ 9]. Although there are 10 elements, only nine comparisons are performed. Because of the way the successive comparisons are made, a large value may move down the array many positions on a single pass, but a small value may move up only one position. On the first pass, the largest value is guaranteed to sink to the bottom element of the array, a[ 9 ]. On the second pass, the second largest value is guaranteed to sink to a[ 8 ]. On the ninth pass, the ninth largest value sinks to a[ 1 ]. This leaves the smallest value in a[ 0 ], so only nine passes are needed to sort a 10-element array.

MULTIPLE-SUBSCRIPTED ARRAYS


A common use of multiple-subscripted arrays is to represent tables of values consisting of rows and columns. To identify an element, we have to specify two subscripts: the first identifies the element's row and the second identifies the element's column.


Example


The following example demonstrates initializing double-subscripted arrays in declarations. the program declares 3 arrays, each with 2 rows and 3 columns. The declaration of array1 provides 6 initializers in two sublists. The first sublist initializes the first row of array to the values 1, 2, and 3; and the second sublist initializes the second row of the array to the values 4, 5, and 6. If the braces around each sublist are removed from the array1 initializer list, the compiler automatically initializes the elements of the first row foloowed by the elements of the second row.


The declaration of array2 provides 5 initializers. The initializers are assigned to the first row then the second row. Any elements that do not have an explicit initializer are initialized to zero automatically.


Example


//Initializing multidimensional arrays
#include <iostream.h>

void printArray( int [][ 3 ] );

int main()
{
   int array1[ 2 ][ 3 ] = { {1,2,3}, {4,5,6} },
       array2[ 2 ][ 3 ] = { 1, 2, 3, 4, 5 },
       array3[ 2 ][ 3 ] = { { 1, 2 }, { 4 } };

   cout << "Values in array1 by row are:" << endl;
   printArray( array1 );

   cout << "Values in array2 by row are:" << endl;
   printArray( array2 );

   cout << "Values in array3 by row are:" << endl;
   printArray( array3 );

   return 0;
}

void printArray( int a[][ 3 ] )

{
   for ( int i = 0; i < 2; i++ ) {

     for ( int j = 0; j < 3; j++ )
      cout << a[ i ][ j ] << ' ';
  
     cout << endl;
   }
}


THE OUTPUT WILL BE:

Values in array1 by row are:
1 2 3
4 5 6
Values in array2 by row are:
1 2 3
4 5 0
Values in array3 by row are:
1 2 0
4 0 0

CHAPTER (5) - POINTERS AND STRINGS
**********************************
Pointer variables contain memory addresses as their values. Normally, a variable directly contains a specific value. A pointer, on the other hand, contains an address of a variable that contains a specific value. A variable directly references a value, and a pointer indirectly references a value. Referencing a value through a pointer is called indirection.


int *countPtr, count;
declares the variable countPtr to be of type int * (i.e., a pointer to an integer value) and means that countPtr points to an object of type integer. Variable count is not a pointer but an integer. Each variable being declared as a pointer must be preceeded by an asterisk(*). Pointers can be declared to point to objects of any data type.


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AFTER TODAY'S CLASS IS OVER, LOOK AT THE ASSIGNMENT.