Arrays in C

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An array is a side by side arrangement of items. Two adjacent items should share a common wall. Biscuits in a packet, and houses in a street are examples of arrays.

Arrays in C

We can create an array of 5 int by writing code like this

int arr[5];

This code declares an array of 5 int. We already know that a compiler allocates a memory address to each variable that it creates. Similarly, an array is laid at a certain memory address. But since two elements share a common wall, the elements of the array will be laid at consequetive memory locations.

Arrays can be created for any data type except functions, void and references. This is an example of creating an array for a char and float types.

char k[10];

float farr[4];

Array Initialization

Arrays can be given initial values at the time of declaration. There is a special syntax for this. This syntax is called the intializer syntax. This is how it can be done.

int arr[3] = {5, 8, 2};

An array of three int has been given initial values. These values serially go into items 1, 2 and 3 of the array. The items of an array are indexed from 0. So the first item has index of 0, the second one has an index of 1, and so on. The above items can be displayed back like this

int main()
{
    int arr[3] = {5, 8, 2};
 
    cout << arr[0] << endl; // prints 5
 
    cout << arr[1] << endl; // prints 8
 
    cout << arr[2] << endl; // prints 2
 
    return 0;
}

If the number of intializers is less than the declared size of the array, the remaining elements get default values of 0, 0.0, 0.0f or '\0' depending on the data type of the array. In the code below, the items at index 2, 3, and 4 get the value of 0, because the default value of an int is 0.

int main()
{
    int arr[5] = {5, 8};
 
    cout << arr[0] << endl; // prints 5
 
    cout << arr[1] << endl; // prints 8
 
    cout << arr[2] << endl; // prints 0

    cout << arr[3] << endl; // prints 0

    cout << arr[4] << endl; // prints 0
 
    return 0;
}

What happens if the number of intializers exceeds the declared size of the array? In that case the compiler gives an error, and the code doesn't compile.

// compiler error
int arr[3] = {5, 8, 2, 8, 8};

Automatic initialization of an array can be done by not giving the size of the array at all. The compiler can deduce the size from the number of elements in the initializer.

// automatic intialization, no error
int arr[] = {5, 8, 2, 8, 8};

Memory Allocation

It is possible to calculate the number of bytes allocated to an array by using the sizeof operator. The memory allocated to an array is also equal to the number of items in the array multiplied by the size of one element. This axoim can be used to programmatically determine the number of elements in an array.

int main()
{
    int arr[] = {5, 8, -9, 0, 33, 274};

    // prints the total allocation to arr 
    cout << sizeof (arr) << endl;

    // prints the same thing
    cout << (6 * sizeof (int)) << endl; 
 
    // number of elements in an array
    int totalElements = sizeof (arr) / sizeof (int);

    cout << "Total elements = " << totalElements << endl;

    return 0;
}

Printing Addresses of the Elements

The array identifier contains the starting address of an array. The address can be printed by printing the array identifier. It should be cast to an int to display it as a base 10 number.

int main()
{
    int arrI[5];
 
    cout << "Array starts at " << (int)arrI << endl;
 
    char arrC[5];
 
    cout << "Array starts at " << (int)arrC << endl;
 
    float arrF[5];
 
    cout << "Array starts at " << (int)arrF << endl;
 

    return 0;
}

Array address can be printed with the printf also. The format specifier %p is used to print an address. The address is printed in hexadecimal form. The specifier %d will print the same address as a base 10 decimal number.

int main()
{
    int arrI[5];
 
    printf("Array starts at %p\n", arrI);
 
    char arrC[5];
 
    printf("Array starts at %p\n", arrC);
 
    float arrF[5];
 
    printf("Array starts at %p\n", arrF);
 
    return 0;
}
 

int main()
{
    int arrI[5];
    
    for(int i = 0; i < 5; i++)
    {
        cout << "Address of item " << i << " = ";
 
        cout << (arrI + i) << endl;
    }
 
    return 0;
}

Pointers and Arrays

Array addresses can be stored in a pointer variable of compatible type. If an array contains int types, then the array address can be stored in an int*. Similarly, if the array contains float, then the address can be stored in a float*.

int main()
{
    int arrI[5];
 
    int* p = arrI;
 
    return 0;
}
 

Characteristics of an Array

These are the important characteristics of an array.

1. Arrays have a fixed size that must be stated at the time of declaration.
2. A large number of variables can be declared easily using the array syntax. It is easy to manage the variables created in this way.
3. Array access is extremely fast because all the elements lie "near by".

Display elements of array

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arr[10];
 
    for (int i = 0; i < 10; i++)
    {
        arr [i] = i;
    }
 
    for (int i = 0; i < 10; i++)
    {
         cout << arr [i] << endl;
    }
 
    return 0;
} 
 

Show elements

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main()
{
    
    int arr[5] = {22,33,44,55,99};
    
    cout << arr[0] << endl; 
    
    cout << arr[4] << endl;
    
    return 0;
    
}

Addition using an array

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arrOne[5] = {8, 7, 2, 0, -9};
 
    int arrTwo[5] = {-8, -7, -2, 0, +9};
 
 
    for (int i = 0; i < 5; i++)
    {
         cout << (arrOne [i] + arrTwo[i]) << endl;
    }
 
    return 0;
}

Arrays and cube

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arr[5] = {3, 5, 7, 1, 4} ;
 
    for(int i = 0; i < 5; i++)
    {
        int cube = arr[i] * arr[i] * arr[i];
 
        cout << "Cube of " ;
        
        cout << arr [i] << " = ";
        
        cout << cube << endl;
    }
 
    return 0;
}

Array element location

 
#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arr[10];
 
    for(int i = 0; i < 10; i++)
    {
        cout << "Address of element " << i << " = ";
 
        cout << (int)(arr + i) << "(base 10); ";
 
        cout << (arr + i) << "(base 16)" << endl;
    }
 
    return 0;
}
 

Print address

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arr[10];
 
    cout << "Without & operator = " << arr << endl; 
 
    cout << "With & operator = " << &arr[0] << endl;
 
    return 0;
} 

Array addresses with a pointer

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int arr[5];
 
    int* p = arr; 
 
    for(int i = 1; i < 5; i++)
    {
        cout << ++p << endl;
    }
 
    return 0;
}
 
 

Address of variable

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main() 
{
    int var = 5;
    
    printf("Value: %d\n",var);
    
    // p is for printing an address
    printf("Address: %p",&var);

    // print address in base 10
    printf("Address: %d",&var);
    
    return 0;
}
 

Character array

#include<iostream>
#include<cstdio> 
 
using namespace std;

int main()
{

    char c[4];

    int i;

    for(i=0; i < 4; i++)
    {

        printf("Address of c[%d]=%p\n",i, &c[i]);
    
    }

    return 0;

}

Swaping with pointers

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
void swap(int *a, int *b)
{ 
 
    int temp;
     
    temp = *a;
    
    *a = *b;
    
    *b = temp;
}
 

int main()
{
 
    int num1 = 5, num2 = 10;
    
    printf("Before swap num1 = %d\n",num1);
    
    printf("Before swap num2 = %d\n",num2);

    swap( &num1, &num2 );
    
    printf("After swap num1 = %d\n",num1);
    
    printf("After swap num2 = %d",num2);
    
    return 0;
        
}
 

Calculate sum

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main()
{
    int arr[5] = {6, 8, -6, 5, 9};
 
    int sum = 0;
 
    for(int i = 0; i < 5; i++)
    {
        sum += arr[i];
    }
 
    cout << "Sum = " << sum << endl;
 
    return 0;
}
 

Even odd

#include<iostream>
#include<cstdio> 
 
using namespace std;
 
int main()
{
    int arr[5] = {3, 6, 7, 8, 11};
 
    for(int i = 0; i < 5; i++)
    {
        cout << (arr[i] % 2 ? "Odd: " : "Even: ") ;
        
        cout << arr[i] << endl;
    }
 
    return 0;
}
 
 

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