for AND and OR operation
else if ( s . size ( ) == 5 ) { int a = s [ 0 ] - 48 , b = s [ 4 ] - 48 , c ; s [ 2 ] == ' & ' ? c = a && b : c = a || b ; arr . push ( ( char ) c + 48 ) ; } } else { arr . push ( str [ i ] ) ; } } return arr . top ( ) ; }