Something like this would do the trick:
max <= a
loc <= 0
for i = 1..49
if a[i] > max
max <= a[i]
loc <= i
Don't forget C arrays are zero based, and int a defines an array from a..a.
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 doesn't exist).
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.