1.
mkdir a1
mkdir b1
mkdir c1
cd a1
mkdir a2
mkdir b2
cd c1
mkdir c2
mkdir d2

2.
useradd aa
passwd aa
useradd bb
passwd bb
useradd cc
passwd cc

groupadd gg
gpasswd –a aa gg
gpasswd –a bb gg
vi /etc/group
cp /etc/group /tmp/file1
chown aa :gg /tmp/file1
chmod 750 /tmp/file1
ls –l
3.
vi chengji.c

include<stdio.h>

main(){
int num;
printf("plz ,input source!");
scanf("%d",&num);
if(num>=90) printf("A");
if(num<90&&num>=80) printf("B");
if(num<80&&num>=70) printf("C");
if(num<70&&num>=60) printf("D");
if(num<60) printf("E");
}
ESC
:wq
gcc -o chengji chengji.c