用C语言写一个学生信息管理系统。

好的，下面是一个简单的学生信息管理系统的C语言代码示例：

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define MAX_NAME_LEN 20
#define MAX_STUDENT_NUM 100

struct student {
    char name[MAX_NAME_LEN];
    int id;
    int score;
};

struct student students[MAX_STUDENT_NUM]; // 学生信息数组
int student_num = 0; // 当前学生数量

// 添加学生信息
void add_student() {
    if (student_num >= MAX_STUDENT_NUM) {
        printf("Error: student list is full!\n");
        return;
    }

    struct student s;
    printf("Enter student name: ");
    scanf("%s", s.name);
    printf("Enter student id: ");
    scanf("%d", &s.id);
    printf("Enter student score: ");
    scanf("%d", &s.score);

    students[student_num++] = s;
    printf("Student added successfully!\n");
}

// 查找学生信息
void find_student() {
    int id;
    printf("Enter student id to search: ");
    scanf("%d", &id);

    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id) {
            printf("Student found!\n");
            printf("Name: %s\n", students[i].name);
            printf("Id: %d\n", students[i].id);
            printf("Score: %d\n", students[i].score);
            return;
        }
    }

    printf("Student not found!\n");
}

// 修改学生信息
void modify_student() {
    int id;
    printf("Enter student id to modify: ");
    scanf("%d", &id);

    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id) {
            printf("Enter new student name (press Enter to skip): ");
            char name[MAX_NAME_LEN];
            getchar(); // 把之前的回车符吃掉
            fgets(name, MAX_NAME_LEN, stdin);
            if (strlen(name) > 1) {
                name[strlen(name)-1] = '\0'; // 把最后的回车符替换为字符串结束符
                strcpy(students[i].name, name);
            }

            printf("Enter new student score (press Enter to skip): ");
            char score_str[10];
            fgets(score_str, 10, stdin);
            if (strlen(score_str) > 1) {
                students[i].score = atoi(score_str);
            }

            printf("Student modified successfully!\n");
            return;
        }
    }

    printf("Student not found!\n");
}

// 删除学生信息
void delete_student() {
    int id;
    printf("Enter student id to delete: ");
    scanf("%d", &id);

    int i;
    for (i = 0; i < student_num; i++) {
        if (students[i].id == id) {
            // 把该学生之后的所有学生信息向前移动一个位置
            int j;
            for (j = i; j < student_num-1; j++) {
                students[j] = students[j+1];
            }

            student_num--;
            printf("Student deleted successfully!\n");
            return;
        }
    }

    printf("Student not found!\n");
}

// 显示所有学生信息
void show_all_students() {
    int i;
    for (i = 0; i < student_num; i++) {
        printf("==================\n");
        printf("Name: %s\n", students[i].name);
        printf("Id: %d\n", students[i].id);
        printf("Score: %d\n", students[i].score);
    }
}

int main() {
    char command;
    while (1) {
        printf("==================\n");
        printf("Commands:\n");
        printf("a: Add student information\n");
        printf("f: Find student information\n");
        printf("m: Modify student information\n");
        printf("d: Delete student information\n");
        printf("s: Show all student information\n");
        printf("q: Quit\n");
        printf("Enter command: ");
        scanf("%s", &command);

        switch(command) {
            case 'a': add_student(); break;
            case 'f': find_student(); break;
            case 'm': modify_student(); break;
            case 'd': delete_student(); break;
            case 's': show_all_students(); break;
            case 'q': return 0;
            default: printf("Invalid command!\n"); break;
        }
    }

    return 0;
}

这个程序可以添加、查找、修改、删除和显示所有学生信息。你可以根据需要进一步扩展功能。