counts number of ones at odd and even positions
int odd_1 = 0 , even_1 = 0 ; int n = st . Length ; for ( int i = 0 ; i < n ; i ++ ) { if ( i % 2 == 0 ) { if ( st [ i ] == '1' ) { even_1 ++ ; } else { even_0 ++ ; } } else { if ( st [ i ] == '1' ) { odd_1 ++ ; } else { odd_0 ++ ; } } }