How to sort a 2d array according to the second column using stl sort function?

The stl sort requires the rvalue of the iterator being passed as the arguments. If you wanna use the sort function, you will have to compile in c++11 and use the array stl to store the array. The code is as follows

#include "bits/stdc++.h"
using namespace std;
bool compare( array<int,2> a, array<int,2> b)
{
    return a[0]<b[0];
}
int main()
{
    int i,j;
    array<array<int,2>, 5> ar1;
    for(i=0;i<5;i++)
    {
        for(j=0;j<2;j++)
        {
            cin>>ar1[i][j];
        }
    }
    cout<<"\n earlier it is \n";
    for(i=0;i<5;i++)
    {
        for(j=0;j<2;j++)
        {
            cout<<ar1[i][j]<<" ";
        }
        cout<<"\n";
    }
    sort(ar1.begin(),ar1.end(),compare);
    cout<<"\n after sorting \n";
    for(i=0;i<5;i++)
    {
        for(j=0;j<2;j++)
        {
            cout<<ar1[i][j]<<" ";
        }
        cout<<"\n";
    }
    return 0;
}

Compiling in c++11 can be done by g++ -std=c++11 filename.cpp -o out. In case you do not want to use c++11 or use the "array" stl, use the std::qsort function. With this you can use the traditional way to define the arrays like int a[10][2]. The code is as follows

#include "bits/stdc++.h"
using namespace std;
int compare( const void *aa, const void  *bb)
{
    int *a=(int *)aa;
    int *b=(int *)bb;
    if (a[0]<b[0])
     return -1;
    else if (a[0]==b[0]) 
    return 0;
    else  
     return 1;

}
int main() 
{
    int a[5][2];
    cout<<"enter\n";
    for(int i=0;i<5;i++)
    {
        for(int j=0;j<2;j++)
        {
            cin>>a[i][j];
        }
        //cout<<"\n";
    }
    cout<<"\n\n";
    qsort(a,5,sizeof(a[0]),compare);
    for(int i=0;i<5;i++)
    {
        for(int j=0;j<2;j++)
        {
            cout<<a[i][j]<<" ";
        }
        cout<<"\n";
    }
    return 0;
   }

Make your own compare function.

See the Beginners guide to std::sort(). http://www.cplusplus.com/articles/NhA0RXSz/