C++ C语言中在getline()函数中使用if语句

这是一个打印最长行的程序.摘自K&amp；R的c编程语言一书.

我的疑问是，代码的必要性是什么.

    if(c == '\n'){
     s[i]=c;
     ++i;
    }

在getLine()函数中.

#include<stdio.h>
# define MAXLINE 1000  /*maximum length of the input line*/

int getLine(char s[],int line);
void copy(char from[],char to[]);

int main(){
    int curr_len; //current line length
    int max_len = 0;  // maximum line length so far

    char curr_line[MAXLINE];             // Current input line
    char longest_line[MAXLINE];     // maximum line saved so far

    while((curr_len = getLine(curr_line,MAXLINE))>0){
        if(curr_len>max_len){
            copy(curr_line,longest_line);  //save the longest line
            max_len = curr_len;
        }
    }
    if(max_len>0){
        printf("%s\n",longest_line);
    }
    return 0;

}

/* getline: read a line into s, return length*/
int getLine(char s[],int maxline){
    int c,i;
    for(i=0;i<maxline-1 && (c = getchar())!=EOF && c!='\n';++i){
        s[i]=c;
        if(c == '\n'){
            s[i]=c;
            ++i;
        }
    }
    s[i]='\0';
    return  i;
}

/* copy: copy 'from' into 'to'; assume to is big enough */
void copy(char from[],char to[]){
    int i=0;
    while((to[i] = from[i])!='\0'){
        ++i;
    }
}

请解释为什么在getLine()函数中使用if语句