Arrays

One Dimensional Array

An array is a collection of data elements of same data type. It is described by a single name and each element of an array is referenced by using array name and its subscript no.

Declaration of Array

Type arrayName[numberOfElements];

For example,
int Age[5] ;
float cost[30];

Initialization of One Dimensional Array

An array can be initialized along with declaration. For array initialization it is required to place the elements separated by commas enclosed within braces.
int A[5] = {11,2,23,4,15};
It is possible to leave the array size open. The compiler will count the array size.
int B[] = {6,7,8,9,15,12};

Referring to Array Elements

In any point of a program in which an array is visible, we can access the value of any of its elements individually as if it was a normal variable, thus being able to both read and modify its value. The format is as simple as:
name[index]

Examples:
cout<<age[4];      //print an array element
age[4]=55;         // assign value to an array element
cin>>age[4];       //input element 4

Using Loop to input an Array from user

int age [10], i ;
for (i=0 ; i<10; i++)
{
  cin>>age[i];
}

Arrays as Parameters

At some moment we may need to pass an array to a function as a parameter. In C++ it is not possible to pass a complete block of memory by value as a parameter to a function, but we are allowed to pass its address.
For example, the following function:
void print(int A[])
accepts a parameter of type "array of int" called A.
In order to pass to this function an array declared as:
int arr[20];
we need to write a call like this:
print(arr);
Here is a complete example: 

#include <iostream.h>
void print(int A[], int length)
{
  for (int n=0; n<length; n++)
    cout << A[n] << " ";
  cout << "\n";
}

int main ()
{
  int arr[] = {5, 10, 15};
  print(arr,3);
  return 0;
}

Basic Operation On One Dimensional Array

Function to traverse the array A

void display(int A[], int n)
{
       cout<<"The elements of the array are:\n";
       for(int i=0;i<n;i++)
              cout<<A[i];
}

Function to Read elements of the array A

void Input(int A[], int n)
{
      cout<<"Enter the elements:";
      for(int i=0;i<n;i++)
            cin>>A[i];
}

Function to Search for an element from A by Linear Search

int Lsearch(int A[], int n, int Data)
{
      int I;
      for(I=0; I<n; I++)
      {
            if(A[I]==Data)
            {
                  cout<<"Data Found at : "<<I;
                  return;
            }
      }
      cout<<"Data Not Found in the array"<<endl;
}

Function to Search for an element from Array A by Binary Search

int BsearchAsc(int A[], int n, int data)
{
       int Mid,Lbound=0,Ubound=n-1,Found=0;
       while((Lbound<=Ubound) && !(Found))
       {
              Mid=(Lbound+Ubound)/2;        //Searching The Item
              if(data>A[Mid])
                     Lbound=Mid+1;
              else if(data<A[Mid])
                     Ubound=Mid-1;
              else
                     Found++;
       }
       if(Found)
              return(Mid+1);        //returning 1ocation, if present
       else
              return(-1);        //returning -1,if not present
}

Function to Sort the array A by Bubble Sort

void BSort(int A[], int n)
{
    int I,J,Temp;
    for(I=0;I<n-1;I++) //sorting
   {
       for(J=0;J<(n-1-I);J++)
            if(A[J]>A[J+1])
           {
               Temp=A[J]; //swapping
               A[J]=A[J+1];
               A[J+1]=Temp;
           }
    }
}

Function to Sort the array ARR by Insertion Sort

void ISort(int A[], int n)
{
       int I,J,Temp;
       for(I=1;I<n;I++) //sorting
       {
           Temp=A[I];
           J=I-1;
           while((Temp<A[J]) && (J>=0))
           {
               A[J+1]=A[J];
               J--;
           }
           A[J+1]=Temp;
       }
}

Function to Sort the array by Selection Sort

void SSort(int A[], int n)
{
    int I,J,Temp,Small;
    for(I=0;I<n-1;I++)
    {
         Small=I;
         for(J=I+1;J<n;J++) //finding the smallest element
         if(A[J]<A[Small])
              Small=J;
         if(Small!=I)
        {
            Temp=A[I]; //Swapping
            A[I]=A[Small];
            A[Small]=Temp;
        }
     }
}

Function to merge A and B arrays of lenghts N and M

void Merge(int A[], int B[], int C[], int N, int M, int &K)
{
      int I=0, J=0;
      K=0;             //Initialisation of counters for A, B, and C
      while (I<N && J<M)
      {
            if (A[I]<B[J])
                  C[K++]=A[I++];
            else if (A[I]>B[J])
                  C[K++]=B[J++];
            else
            {
                  C[K++]=A[I++];
                  J++;
            }
      }
      for (int T=I;T<N;T++)
            C[K++]=A[T];
      for (T=J;T<M;T++)
            C[K++]=B[T];
}

Two Dimensional Array

It is a collection of data elements of same data type arranged in rows and columns (that is, in two dimensions).

Declaration of Two-Dimensional Array

Type arrayName[numberOfRows][numberOfColumn];

For example,
int Sales[3][5];

Initialization of Two-Dimensional Array

An two-dimensional array can be initialized along with declaration. For two-dimensional array initialization, elements of each row are enclosed within curly braces and separated
by commas. All rows are enclosed within curly braces.
int A[4][3] = {{22, 23, 10},
              {15, 25, 13},
              {20, 74, 67},
              {11, 18, 14}};

Referring to Array Elements

To access the elements of a two-dimensional array, we need a pair of indices: one for
the row position and one for the column position. The format is as simple as:
name[rowIndex][columnIndex]

Examples:
cout<<A[1][2];      //print an array element
A[1][2]=13;         // assign value to an array element
cin>>A[1][2];       //input element

Using Loop to input an Two-Dimensional Array from user

int mat[3][5], row, col ;
for (row = 0; row < 3; row++)
  for (col = 0; col < 5; col++)
    cin >> mat[row][col];

Arrays as Parameters

Two-dimensional arrays can be passed as parameters to a function, and they are passed by reference. When declaring a two-dimensional array as a formal parameter, we can omit the size of the first dimension, but not the second; that is, we must specify the number of columns. For example:
   void print(int A[][3],int N, int M)
In order to pass to this function an array declared as:
   int arr[4][3];
we need to write a call like this:
   print(arr);
Here is a complete example: 

#include <iostream.h>
void print(int A[][3],int N, int M)
{
  for (R = 0; R < N; R++)
    for (C = 0; C < M; C++)
       cout << A[R][C];
}

int main ()
{
  int arr[4][3] ={{12, 29, 11},
                  {25, 25, 13},
                  {24, 64, 67},
                  {11, 18, 14}};
  print(arr,4,3);
  return 0;
}

Function to read the array A

void Read(int A[][20], int N, int M)
{
  for(int R=0;R<N;R++)
    for(int C=0;C<M;C++)
    {
      cout<<"(R<<','<<")?";
      cin>>A[R][C];
     }
}

Function to display content of a two dimensional array A

void Display(int A[][20],int N, int M)
{
  for(int R=0;R<N;R++)
  {
     for(int C=0;C<M;C++)
        cout<<setw(10)<<A[R][C];
     cout<<endl;
   }
}

Function to find the sum of two dimensional arrays A and B

void Addition(int A[][20], int B[][20],int N, int M)
{
  for(int R=0;R<N;R++)
    for(int C=0;C<M;C++)
      C[R][C]=A[R][C]+B[R][C];
}

Function to multiply two dimensional arrays A and B of order NxL and LxM

void Multiply(int A[][20], int B[][20], int C[][20],int N, int L, int M)
{
  for(int R=0;R<N;R++)
   for(int C=0;C<M;C++)
   {
      C[R][C]=0;
      for(int T=0;T<L;T++)
        C[R][C]+=A[R][T]*B[T][C];
    }
}

Function to find & display sum of rows & sum of cols. of a 2 dim. array A

void SumRowCol(int A[][20], int N, int M)
{
  for(int R=0;R<N;R++)
  {
     int SumR=0;
     for(int C=0;C<M;C++)
       SumR+=A[R][C];
     cout<<"Row("<<R<<")="<<SumR<<endl;
   }
  for(int R=0;R<N;R++)
  {
    int SumR=0;
    for(int C=0;C<M;C++)
      SumR+=A[R][C];
    cout<<"Row("<<R<<")="<<SumR<<endl;
   }
}

Function to find sum of diagonal elements of a square matrix A

void Diagonal(int A[][20], int N, int &Rdiag, int &LDiag)
{
  for(int I=0,Rdiag=0;I<N;I++)
    Rdiag+=A[I][I];
  for(int I=0,Ldiag=0;I<N;I++)
    Ldiag+=A[N-I-1][I];
}

Function to find out transpose of a two dimensional array A

void Transpose(int A[][20], int B[][20],int N, int M)
{
  for(int R=0;R<N;R++)
    for(int C=0;C<M;C++)
       B[R][C]=A[C][R];
}

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