binary to decimal

[hkrishnan81]

Hi friends,
I am trying to find the decimal form of a binary number and I have done till here and am not able to detect where I am going wrong .
#include<iostream.h>
#include<conio.h>
void main()
{
clrscr();
int a,arr[20],ar[20],sum=0;
cout<<"enter the digits in the decimal form";
cin>>a;
cout<<"enter the number in decimal form";
for(int i=0;i<=a;i++)
{
cin>>arr[i];
}
for(int j=a-1;j>=0;j--)
{
ar[i]=(arr[i]*2)^j;
sum=sum+ar[i];
}
cout<<sum;
getch();
}Can anybody help..???

[Chervil]

The code does not compile

#include<iostream.h>
#include<conio.h>
void main()
{
    clrscr();

    int a,arr[20],ar[20],sum=0;

    cout<<"enter the digits in the decimal form";
    cin>>a;
    cout<<"enter the number in decimal form";
    for(int i=0;i<=a;i++)
    {
        cin>>arr[i];
    }

    for(int j=a-1;j>=0;j--)
    {
        ar[i]=(arr[i]*2)^j;
        sum=sum+ar[i];
    }

    cout<<sum;

    getch();
}

At line 19, i is undefined.
If your compiler accepts this with no error, then I'd recommend upgrading to a newer more standard compiler.

I've not tried to understand your algorithm, no comments there.
However the use of the bitwise XOR operator ^ looks a bit suspicious.