Learn C++ - C++ Array

• « Previous
• Next »

An array is a data form that can hold several values, all of one type.

To create an array, you use a declaration statement.

For example, the following declaration creates an array named months that has 12 elements, each of which can hold a type short value:

short months[12];     // creates array of 12 short 

Each element, in essence, is a variable that you can treat as a simple variable.

This is the general form for declaring an array:

typeName arrayName [arraySize]; 

The expression arraySize, which is the number of elements, must be an integer constant.

Example

The following code demonstrates a few properties of arrays, including declaring an array, assigning values to array elements, and initializing an array.

#include <iostream> 
using namespace std; 
int main() /*  w w  w  . j a  v  a  2s.co m*/
{ 
     int my_array[3];    // creates array with three elements 
     my_array[0] = 7;    // assign value to first element 
     my_array[1] = 8; 
     my_array[2] = 6; 

     int my_value[3] = {20, 30, 5}; // create, initialize array 
     cout << my_array[0] + my_array[1] + my_array[2] << endl; 
     cout << my_array[1] << " my_array costs "; 
     cout << my_value[1] << ".\n"; 
     int total = my_array[0] * my_value[0] + my_array[1] * my_value[1]; 
     total = total + my_array[2] * my_value[2]; 
     cout << total << " cents.\n"; 

     cout << "\nSize of my_array array = " << sizeof my_array; 
     cout << " bytes.\n"; 
     cout << "Size of one element = " << sizeof my_array[0]; 
     cout << " bytes.\n"; 
     return 0; 
} 

The code above generates the following result.

Initialization Rules for Arrays

You can use the initialization form only when defining the array.

int cards[4] = {3, 6, 8, 10};       // okay 
int hand[4];                        // okay 

When initializing an array, you can provide fewer values than array elements.

If you partially initialize an array, the compiler sets the remaining elements to zero.

It's easy to initialize all the elements of an array to zero-just explicitly initialize the first element to zero:

If you leave the square brackets [] empty when you initialize an array, the C++ compiler counts the elements for you.

Suppose, for example, that you make this declaration:

The compiler makes things an array of four elements.

Second, you can use empty braces to set all the elements to 0:

unsigned int counts[10] = {};  // all elements set to 0 
float balances[100] {};        // all elements set to 0 

Example: Initializing an array's elements to zeros and printing the array.

#include <iostream> 
#include <iomanip> 
using namespace std; 
/* w  ww .ja  v  a  2  s. com*/
int main() { 
    int n[ 10 ]; // n is an array of 10 integers 

    // initialize elements of array n to 0 
    for ( int i = 0; i < 10; ++i ) 
       n[ i ] = 0; // set element at location i to 0 

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

    // output each array element's value 
    for ( int j = 0; j < 10; ++j ) 
       cout << setw( 7 ) << j << setw( 13 ) << n[ j ] << endl; 
}

The code above generates the following result.

Initializing an array in a declaration

#include <iostream> 
#include <iomanip> 
using namespace std; 
//  ww w .j a  v  a 2 s .c  om
int main() { 
    // use initializer list to initialize array n 
    int n[ 10 ] = { 32, 27, 64, 18, 95, 14, 90, 70, 60, 37 }; 

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

    // output each array element's value 
    for ( int i = 0; i < 10; ++i ) 
        cout << setw( 7 ) << i << setw( 13 ) << n[ i ] << endl; 
}

The code above generates the following result.

Two-Dimensional Array

For a two-dimensional array, each element is itself an array.

Thus, the initialization consists of a comma-separated series of one-dimensional initializations, all enclosed in a set of braces:

int maxtemps[4][5] =   // 2-D array 
{ 
   {96, 100, 87, 101, 105},   // values for maxtemps[0] 
   {96, 98, 91, 107, 104},    // values for maxtemps[1] 
   {97, 101, 93, 108, 107},   // values for maxtemps[2] 
   {98, 103, 95, 109, 108}    // values for maxtemps[3] 
}; 

The following code shows how to use nested loops and 2-D array.

#include <iostream> 
const int Cities = 5; 
const int Years = 4; 
int main() 
{ 
     using namespace std; 
     const char * cities[Cities] =   // array of pointers 
     {                               // to 5 strings 
          "A", 
          "AA", 
          "AAA", 
          "AAAA", 
          "AAAAA" 
     }; 

     int maxtemps[Years][Cities] =   // 2-D array 
     { 
          {96, 100, 87, 101, 105},   // values for maxtemps[0] 
          {96, 98, 91, 107, 104},    // values for maxtemps[1] 
          {97, 101, 93, 108, 107},   // values for maxtemps[2] 
          {98, 103, 95, 109, 108}    // values for maxtemps[3] 
     }; 

     cout << "Maximum temperatures for 2008 - 2011\n\n"; 
     for (int city = 0; city < Cities; ++city) 
     { 
         cout << cities[city] << ":\t"; 
         for (int year = 0; year < Years; ++year) 
              cout << maxtemps[year][city] << "\t"; 
         cout << endl; 
     } 
     return 0; 
} 

• Next »
• « Previous