process carry
for ( int i = n - 2 ; i >= 0 ; i -- ) { if ( c [ i ] == '9' ) c [ i ] = '0' ; else { int t = c [ i ] - '0' + 1 ; c [ i ] = ( char ) ( 48 + t ) ; break ; } } } string s1 = c ; if ( s1 [ 0 ] == '0' ) s1 = "1" + s1 ;