Something like this would do the trick:
max <= a[0][0]
loc <= 0
for i = 1..49
  if a[i][0] > max
    max <= a[i][0]
    loc <= i
Don't forget C arrays are zero based, and int a[50] defines an array from a[0]..a[49].
So your loop above starting from 1 and ending at n will not work (actually it will work for all n<=1<=49 but at n=50 there will be undefined behaviour because a[50] doesn't exist).

for (i=1;i<=n;i++)
  for (j=1;j<=n;j++)
  cout <<"Row "<<i<<", Column "<<j<<"\n";
  cin >> a[i][j];
Hmm, at n=50 that will be 2500 values. This will be spectacularly tedious. Are the array values in a file anywhere? As a starting point this is fine but if the values are in a file you'll need to extend the code to read the values from a file instead.