如何通过以结构数组作为参数的此函数返回正确的值？

我正在学习StructuresC语言，并尝试编写此问题的解决方案-

创建一个结构来指定以下给定学生的数据：卷号，姓名，系，课程，入学年份。

假设班上学生人数不超过5。（a）编写一个函数，以打印特定年份加入的所有学生的姓名。（b）编写函数以打印给出了卷号的学生的数据。

接下来给出我的代码，并简要描述程序中的各个组件，然后再给出问题的根源-

#include<stdio.h>
struct student
{
    int roll_no;
    char name[20];
    char department[30];
    char course[20];
    int year_joined;
};

void main()
{
    struct student s[5];
    int i=0,choice;

    printf("\n Enter the following information for each student: \n");
    printf("\n Roll No., Name, Department, Course, Year of Joining\n");
    for(i=0;i<=4;i++)
    scanf("%d %s %s %s %d", &s[i].roll_no, &s[i].name, &s[i].department, &s[i].course, &s[i].year_joined);



    printf("\n Please choose from the following options :\n");
    printf("\n 1. Print names of students who joined in a given year.");
    printf("\n 2. Print data of all students whose roll.no is given.");
    scanf("%d",&choice);
    switch(choice)
    {
        case 1: display_names(s);
                break;
        case 2: student_data(s);
                break;

        default: printf("\n Incorrect choice, please try again.");      
    }


}

void display_names(struct student p[])
{
    int i,count=0;
    int year;
    printf("\n Enter the year you wish to search student info. for : \n");
    scanf("%d",&year);
    for(i=0;i<=4;i++)
    {
        if(p[i].year_joined==year)
        {

    //printf("%d %s %s %s %d", p[i].roll_no, p[i].name, p[i].department, p[i].course, p[i]. year_joined);
    count++;
    printf("\n Student Name: %s\n", p[i].name);
        }

    }
    printf("\n Total Number of students who joined in the year %d is %d\n", year,count);
    if(count==0)
    printf("\n No match found.");
}


void student_data(struct student st[])
{   
    int i,count=0;
    int roll;
    printf("\n Enter roll number of the student: \n");
    scanf("%d",&roll);
    for(i=0;i<=4;i++)
    {
        if(st[i].roll_no=roll)
        {
            count++;
            printf("\n Student Data: Roll No. Name Department Course Year of Joining \n");
            printf("\n %d    %s    %s      %s %d", st[i].roll_no, st[i].name, st[i].department, st[i].course,st[i].year_joined);
            break;


        }
    }

    if(count==0)
    printf("\n No matching Roll Numbers found\n");
}

这是该程序的简要说明-

1. 由于需要将有关多个学生的信息存储在结构中，因此我创建了一个结构数组。结构struct student是在最开始就定义的，而数组是在main-struct student s[5]
2. 通过scanf()内部接受用户输入来初始化该结构main()。这switch两个功能有两种情况，请在问题中提出：display_names(s) and student_data(s)
3. display_names（s）函数在main中调用，并在其外部定义。该函数接受astructure array并要求用户输入年份。它遍历初始化数组并搜索用户输入的输入（加入年份）。进行比赛时，它会打印出当年加入的所有学生的姓名。这是此功能的示例输出-

*

**Enter the following information for each student:
 Roll No., Name, Department, Course, Year of Joining
10 Tim CS MS 2013
20 Shane CS MS 2013
30 John EE ME 2013
40 Mark MECH MS 2013
50 Matt EE ME 2010
 Please choose from the following options :
 1. Print names of students who joined in a given year.
 2. Print data of all students whose roll.no is given.1
 Enter the year you wish to search student info. for :
2013
 Student Name: Tim
 Student Name: Shane
 Student Name: John
 Student Name: Mark
 Total Number of students who joined in the year 2013 is 4**

*

此功能工作正常。

问题出在下一个函数中student_data()。与第一个函数类似，它接受结构数组作为输入。我设计该函数的方式-想法是循环遍历数组，直到找到等于用户输入的滚动号为止。如果有比赛，它将打印出该特定学生本身的详细信息。但是，就目前情况而言，此函数始终会打印数组中的第一个条目，我似乎无法理解为什么。我已经添加了break的if statement，但它似乎没有任何区别。

这是一个示例输出-

Enter the following information for each student:
 Roll No., Name, Department, Course, Year of Joining
10 Tim CS MS 2013
20 Shane CS MS 2013
30 John EE ME 2013
40 Mark MECH MS 2013
50 Matt EE ME 2010
 Please choose from the following options :
 1. Print names of students who joined in a given year.
 2. Print data of all students whose roll.no is given.2
 Enter roll number of the student:
40
 Student Data: Roll No. Name Department Course Year of Joining
 40    Tim    CS      MS 2013

能否请您说出我在第二个功能中出了什么问题？