C# 0 The Complete Reference

PART I

C h a p t e r   7 :  

A r r a y s   a n d   S t r i n g s  

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PART IPART I

Boundaries Are Enforced

Array boundaries are strictly enforced in C#; it is a runtime error to overrun or underrun 

the ends of an array. If you want to confirm this for yourself, try the following program that 

purposely overruns an array:

// Demonstrate an array overrun.

using System;

class ArrayErr {

  static void Main() {

    int[] sample = new int[10];

    int i;

    // Generate an array overrun.

    for(i = 0; i < 100; i = i+1)

      sample[i] = i;

  }

}

As soon as 

i

 reaches 10, an 

IndexOutOfRangeException

 is generated and the program is 

terminated. (See Chapter 13 for a discussion of exceptions and exception handling.)

Multidimensional Arrays

Although the one-dimensional array is the most commonly used array in programming, 

multidimensional arrays are certainly not rare. A 

multidimensional array

 is an array that has 

two or more dimensions, and an individual element is accessed through the combination 

of two or more indices.

Two-Dimensional Arrays

The simplest form of the multidimensional array is the two-dimensional array. In a two-

dimensional array, the location of any specific element is specified by two indices. If you 

think of a two-dimensional array as a table of information, one index indicates the row, the 

other indicates the column.

To declare a two-dimensional integer array 

table

 of size 10, 20, you would write

int[,] table = new int[10, 20];

Pay careful attention to the declaration. Notice that the two dimensions are separated from 

each other by a comma. In the first part of the declaration, the syntax

[,]

indicates that a two-dimensional array reference variable is being created. When memory is 

actually allocated for the array using 

new

, this syntax is used:

int[10, 20]

This creates a 10×20 array, and again, the comma separates the dimensions.

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T h e   C #   L a n g u a g e

To access an element in a two-dimensional array, you must specify both indices, 

separating the two with a comma. For example, to assign the value 10 to location 3, 5 

of array 

table

, you would use

table[3, 5] = 10;

Here is a complete example. It loads a two-dimensional array with the numbers 1 

through 12 and then displays the contents of the array.

// Demonstrate a two-dimensional array.

using System;

class TwoD {

  static void Main() {

    int t, i;

    int[,] table = new int[3, 4];

    for(t=0; t < 3; ++t) {

      for(i=0; i < 4; ++i) {

        table[t,i] = (t*4)+i+1;

        Console.Write(table[t,i] + " ");

      }

      Console.WriteLine();

    }

  }

}

In this example, 

table[0, 0]

 will have the value 1, 

table[0, 1]

 the value 2, 

table[0, 2]

 the 

value 3, and so on. The value of 

table[2, 3]

 will be 12. Conceptually, the array will look like 

the one shown in Figure 7-1.

N

OTE

N

OTE

If you have previously programmed in C, C++, or Java, be careful when declaring or accessing 

multidimensional arrays in C#. In these other languages, array dimensions and indices are 

specified within their own set of brackets. C# separates dimensions using commas.

Arrays of Three or More Dimensions

C# allows arrays with more than two dimensions. Here is the general form of a 

multidimensional array declaration:

type

[,

...

,]

 name = 

new

 type

[

size1

,

size2

, ..., 

sizeN

];

F

IGURE

 7-1 

A conceptual view 

of the 

table

 array 

created by the 

TwoD

 program

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