1028 List Sorting 字符串比较的坑点

1028 List Sorting

Excel can sort records according to any column. Now you are supposed to imitate this function.

Input Specification:

Each input file contains one test case. For each case, the first line contains two integers N (≤10^​5) and C, where N is the number of records and C is the column that you are supposed to sort the records with. Then N lines follow, each contains a record of a student. A student’s record consists of his or her distinct ID (a 6-digit number), name (a string with no more than 8 characters without space), and grade (an integer between 0 and 100, inclusive).

Output Specification:

For each test case, output the sorting result in N lines. That is, if C = 1 then the records must be sorted in increasing order according to ID’s; if C = 2 then the records must be sorted in non-decreasing order according to names; and if C = 3 then the records must be sorted in non-decreasing order according to grades. If there are several students who have the same name or grade, they must be sorted according to their ID’s in increasing order.

Sample Input 1:

3 1
000007 James 85
000010 Amy 90
000001 Zoe 60

Sample Output 1:

000001 Zoe 60
000007 James 85
000010 Amy 90

Sample Input 2:

4 2
000007 James 85
000010 Amy 90
000001 Zoe 60
000002 James 98

Sample Output 2:

000010 Amy 90
000002 James 98
000007 James 85
000001 Zoe 60

Sample Input 3:

4 3
000007 James 85
000010 Amy 90
000001 Zoe 60
000002 James 90

Sample Output 3:

000001 Zoe 60
000007 James 85
000002 James 90
000010 Amy 90

先放AC代码

#include <algorithm>
#include <cstring>
#include <cstdio>
using namespace std;
struct Grade{
    int id; //id为6位
    char name[10];
    int score;
}grade[100010];
int n, c;
bool cmp(Grade a,Grade b){
    if(c == 1)
        return a.id < b.id;
    else if(c == 2)
        return strcmp(a.name,b.name) != 0 ? strcmp(a.name,b.name) < 0 : a.id < b.id;
    else if(c == 3)
        return a.score != b.score ? a.score < b.score : a.id < b.id;
}
int main(){
      //n为记录个数，c为排序字段
    scanf("%d%d",&n,&c);
    for (int i = 0; i < n; ++i) {
        scanf("%d %s %d",&grade[i].id,grade[i].name,&grade[i].score);
    }
    sort(grade,grade + n,cmp);
    //输出
    for (int i = 0; i < n; ++i) {
        printf("%06d %s %d\n",grade[i].id,grade[i].name,grade[i].score);
    }
}

此处第一遍做时比较函数cmp写为以下形式
return a.name != b.name ? a.name < b.name : a.id < b.id;
题目所给的测试用例始终不能通过。查阅资料得知
C语言中的字符串是不能直接比较大小的，而C++中的string类型的字符串才能进行字符串的比较。具体细节如下。
具体细节：

1、C语言的字符串的实质是一个字符数组中存储的字符序列，如果直接比较大小相当于比较了两个字符串的首地址的大小，毫无意义。

2、C语言的字符串需要通过strcmp函数进行比较大小。
int strcmp(const char *str1, const char *str2)
返回值 = 0 ，两字符串相等
> 0，str1 大于 str2
< 0，str1 小于 str2

3、C++添加的string字符串是一个类，该类对运算符>、<和==进行了重载，能够直接比较两个字符串的大小。（运算符重载技术）

4、建议在C++中尽量使用string字符串，简单，且不容易出错。
参考资料：https://www.cnblogs.com/wx2247516223/p/10022408.html