INPUT statement有三种控制指针的方式：
1 column pointer controls: reset the pointer's column position when the data values in the data records are read, such as @, +n
2 line pointer controls: reset the pointer's line position when the data values in the data records are read, such as #n, slash(/)
3 line-hold specifiers: hold an input record in the input buffer so that another INPUT statement can process it. By default, the INPUT statement releases the previous record and reads another record, such as @ & @@

Pointer Controls:
@n   go to column n
+n   move the pointer n positions
@    hold the current input line and re-read certain variables.
@@    useful when each input line contains values for several observations
/      skip to the next line of raw data
#n    stands for the number of the line of raw data for that observation