c语言学生管理系统代码要求在原有的学生表中增删学生，学生索引文件也会跟着变化，修改学生信息，按学号查找学生，实现清屏功能

以下是一个示例的C语言学生管理系统代码，满足您的要求，并添加了清屏功能：

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

typedef struct {
    char studentID[10];
    char name[20];
    int age;
} Student;

void clearScreen() {
    system("clear"); // for Linux/Mac
    //system("cls"); // for Windows
}

void addStudent(FILE *dataFile, FILE *indexFile) {
    Student newStudent;
    
    printf("Enter student ID: ");
    scanf("%s", newStudent.studentID);
    printf("Enter student name: ");
    scanf("%s", newStudent.name);
    printf("Enter student age: ");
    scanf("%d", &newStudent.age);

    fseek(dataFile, 0, SEEK_END);
    fwrite(&newStudent, sizeof(Student), 1, dataFile);
    
    fprintf(indexFile, "%s\n", newStudent.studentID);
    
    printf("Student added successfully.\n");
}

void deleteStudent(FILE *dataFile, FILE *indexFile) {
    char studentID[10];
    char line[100];
    FILE *tempIndexFile = fopen("temp_index.txt", "w");
    FILE *tempDataFile = fopen("temp_data.bin", "wb");
    
    printf("Enter student ID to delete: ");
    scanf("%s", studentID);
    
    rewind(indexFile);
    while (fgets(line, sizeof(line), indexFile)) {
        if (strncmp(line, studentID, strlen(studentID)) != 0) {
            fputs(line, tempIndexFile);
        }
        else {
            fseek(dataFile, ftell(dataFile), SEEK_SET);
            fwrite("\0", sizeof(Student), 1, dataFile); // mark as deleted
        }
    }
    
    fclose(indexFile);
    fclose(dataFile);
    fclose(tempIndexFile);
    fclose(tempDataFile);
    
    remove("students_index.txt");
    remove("students_data.bin");
    rename("temp_index.txt", "students_index.txt");
    rename("temp_data.bin", "students_data.bin");
    
    indexFile = fopen("students_index.txt", "r");
    dataFile = fopen("students_data.bin", "ab+");
    
    printf("Student deleted successfully.\n");
}

void modifyStudent(FILE *dataFile, FILE *indexFile) {
    char studentID[10];
    Student newStudent;
    
    printf("Enter student ID to modify: ");
    scanf("%s", studentID);
    
    while (fread(&newStudent, sizeof(Student), 1, dataFile)) {
        if (strncmp(newStudent.studentID, studentID, strlen(studentID)) == 0) {
            printf("Enter new student name: ");
            scanf("%s", newStudent.name);
            printf("Enter new student age: ");
            scanf("%d", &newStudent.age);
            
            fseek(dataFile, -sizeof(Student), SEEK_CUR);
            fwrite(&newStudent, sizeof(Student), 1, dataFile);
            
            printf("Student modified successfully.\n");
            return;
        }
    }
    
    printf("Student not found.\n");
}

void searchStudent(FILE *dataFile, FILE *indexFile) {
    char studentID[10];
    Student foundStudent;
    
    printf("Enter student ID to search: ");
    scanf("%s", studentID);
    
    while (fread(&foundStudent, sizeof(Student), 1, dataFile)) {
        if (strncmp(foundStudent.studentID, studentID, strlen(studentID)) == 0) {
            printf("Student ID: %s\n", foundStudent.studentID);
            printf("Name: %s\n", foundStudent.name);
            printf("Age: %d\n", foundStudent.age);
            return;
        }
    }
    
    printf("Student not found.\n");
}

void displayStudents(FILE *dataFile, FILE *indexFile) {
    char studentID[10];
    Student student;
    
    rewind(indexFile);
    while (fgets(studentID, sizeof(studentID), indexFile)) {
        fseek(dataFile, atoi(studentID) * sizeof(Student), SEEK_SET);
        fread(&student, sizeof(Student), 1, dataFile);
        
        if (strlen(student.studentID) > 0) {
            printf("Student ID: %s\n", student.studentID);
            printf("Name: %s\n", student.name);
            printf("Age: %d\n", student.age);
            printf("-----------------------\n");
        }
    }
}

int main() {
    FILE *dataFile = fopen("students_data.bin", "ab+");
    FILE *indexFile = fopen("students_index.txt", "a+");
    int choice;
    
    if (dataFile == NULL || indexFile == NULL) {
        printf("Error opening file.\n");
        return 1;
    }
    
    while (1) {
        clearScreen();
        printf("----- Student Management System -----\n");
        printf("1. Add student\n");
        printf("2. Delete student\n");
        printf("3. Modify student\n");
        printf("4. Search student\n");
        printf("5. Display all students\n");
        printf("0. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        
        switch (choice) {
            case 1:
                addStudent(dataFile, indexFile);
                break;
            case 2:
                deleteStudent(dataFile, indexFile);
                break;
            case 3:
                modifyStudent(dataFile, indexFile);
                break;
            case 4:
                searchStudent(dataFile, indexFile);
                break;
            case 5:
                displayStudents(dataFile, indexFile);
                break;
            case 0:
                fclose(dataFile);
                fclose(indexFile);
                return 0;
            default:
                printf("Invalid choice. Please try again.\n");
        }
        
        getchar(); // clear newline character
        printf("Press enter to continue...");
        getchar();
    }
    
    return 0;
}

请注意，该示例代码使用了两个文件（students_data.bin 和 students_index.txt）来存储学生信息和学生索引。students_data.bin 文件存储了学生结构体的二进制数据，students_index.txt 文件存储了学生的索引信息（学生ID）。每个学生的信息在文件中占据一块固定大小的空间，可在文件中随机访问。删除学生时，将其对应的数据块标记为删除状态，而不是实际删除。这种方式可以在一定程度上减少文件的碎片化，并提高文件的读取效率。

此外，本示例还添加了清屏功能，使用 `clearScreen()` 函数在终端中清除屏幕内容。请根据您的操作系统选择适用的清屏命令（Linux/Mac 上为 `clear`，Windows 上为 `cls`）。

请根据您的实际需求进行修改和扩展。