问答题

已知C源程序如下：
/*A simple mailing list example using an array of structures. */
# 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()；/*initialize the structure array*/
for(;;)
choice=menu_select();
switch(choice)
case 1:enter();
break;
case 2:deleteAddr();
break;
case 3:list();
break;
case 4:exit(0);


return 0;

/*Initialize the list.*/
void initlist(void)

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

/*Get a menu selection. */
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\")
do
printf("\nEnter your choice:");
gets(s);
c= atoi(s);
while(c＜1 || c＞4);
return c;

/*Input addresses into the list. */
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);

/*Find an unused structure. */
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;

/*Delete an address. */
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;

/*Display the list on the screen. */
void list(void)

register int t;
for(t=0; t＜MAX; ++t)
if(addr_list[t]. name[0])
printf("%s\n", addr_list[t]. 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");

画出main函数的控制流程图；