main.cpp

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#include <iostream>
using namespace std;
int main()
{
    int i,j,k,l;
    for(i=1;i<=5;i++)
    {
        for(j=4;j>=i;j--)
        {
            cout<<" ";
        }
        for(k=1;k<=i;k++) // divide the triangles according to your convenience and then try to see first digit of all is variables or not and then write intialization expression
        {
            cout<<k;
        }
        for(l=i-1;l>=1;l--)// see variables and according to that change the intialisation statement
        {
            cout<<l;
        }
        cout<<endl;
    }
    return 0;
}