已知C源程序如下：
/* A 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 init_list(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\n");
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 anunused 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；