这样就不用显式地转化为字符型了:
data a;
num=123456789012345678;
logn=int(log10(num))+1;
start=6; length=4;
x=left(mod(int(num/10**(logn-start-length+1)),10**length));
put x=;
start=7; length=6;
x=left(mod(int(num/10**(logn-start-length+1)),10**length));
put x=;
keep num x;
run;