已知C源程序如下：
/*一个使用结构体数组的简单地址列表*/
# include ＜stdion.h＞
# include ＜stdlib.h＞
define MAX 4
struct addr
char name[30];
char street[40];
char city[20];
unsigned long int zip;
addr list [MAX] ;
void init_list (void), enter (void);
void deleteAddr(void), list(void);
int menu select (void), find free (void);
int main (void)

char choice;
init_list();/ *初始化结构体数组*/
for(;;)
choice=menu_select();
switch (choice)
case 1:enter();
break;
case 2:deleteAddr();
break;
case 3:list();
break;
case 4:exit(0);


return 0

/*初始化列表*/
void init_list (void)

register int t;
for(t=0;t＜MAX;++t)addr_list[t].name[0]=\0;

/ *获取菜单选择* /
int menu_select (void)

char s[80];
int c;
printf("1. Enter a name\n");
printf("2. Delete a name\n");
printf("3. List the file\n") ;
printf("4. Quit\n") ;
do
printf("\nEnter your choice:");
gets (s);
c=atoi (s);
while(c＜1| | c＞4);
return c;

/ *增加地址* /
void enter (void)

int slot;
char s[80];
slot=find_free ();
if (slot==-1)
printf("\nList Full") ;
return;

printf("Enter name:");
gets (addr_list [slot] .name);
printf("Enter street:");
gets (addr_list[slot]. street);
printf("Enter city:");
gets(addr_list[slot]. city);
printf("Enter zip:");
gets (s);
addr_list[slot] .zip=strtoul(s, \0,10);

/*查找未用结构*/
int find_free (void)

register int t;
for(t=0; addr_list [t]. name[0] ＆＆t＜MAX;++t);
if(t==MAX) return-1; / * no slots free * /
return t;

/*删除地址*/
void deleteAddr(void)

register int slot;
char s[80];
printf("enter record # :");
gets (s);
slot=atoi(s);
if(slot＞=0 ＆＆ slot＜MAX)
addr_list [slot]. name[0]:\0;

/ *在屏幕上显示列表*/
void list (void)

register int t;
for(t=0;t＜MAX;++t)
if (addr_list [t]. name[0])
printf ("%s\n", addr_list It] . name);
printf("%s\n",addr_list[t] .street);
printf("%s\n",addr list[t] .city);
printf ("%lu\n\n", addr_list [t]. zip);


printf ("\n\n");

设计一组测试用例，使该程序所有函数的语句覆盖率尽量达到100%。如果认为该程序的语句覆盖率无法达到100%，则说明原因。