新手一个正在《c程序设计语言》书上有个程序写不出来求指导

#include <stdio.h>

#define MAXLINE 1000 /* maximum input line size */

int getline(char line[], int maxline); //自己编写getline()函数，接收整行字符串
void copy(char to[], char from[]); //和c语言库函数strcpy()实现同样的功能。

/* print longest input line */
int main(void)
{
int len; /* current line length */
int max; /* maximum length seen so far */
char line[MAXLINE]; /* current input line */
char longest[MAXLINE]; /* longest line saved here */

max = 0;

while((len = getline(line, MAXLINE)) > 0)
{
printf("%d: %s", len, line);

if(len > max)
{
max = len;
copy(longest, line);
}
}
if(max > 0)
{
printf("Longest is %d characters:\n%s", max, longest);
}
printf("\n");
return 0;
}

/* getline: read a line into s, return length */
int getline(char s[], int lim)
{
int c, i, j;

for(i = 0, j = 0; (c = getchar())!=EOF && c != '\n'; ++i)
{
if(i < lim - 1)
{
s[j++] = c;
}
}
if(c == '\n')
{
if(i <= lim - 1)
{
s[j++] = c;
}
++i;
}
s[j] = '\0';
return i;
}

/* copy: copy 'from' into 'to'; assume 'to' is big enough */
void copy(char to[], char from[])
{
int i;

i = 0;
while((to[i] = from[i]) != '\0')
{
++i;
}
}
写出来但ctrl+F5没对应的功能这是为什么