写出c语言代码实现完成单处理器系统中的进程调度，要求实现时间片轮转、优先数、最短进程优 先和最短剩余时间优先四种调度算法。实验具体包括：首先确定进程控制块的内容，进程控 制块的组成方式；然后完成进程创建原语和进程调度原语；最后编写主函数对所作工作进行 测试。 模拟程序只对你所设置的“虚拟 PCB”进行相应的调度模拟操作，即每发生“调度” 时，显示出当前运行进程的“进程标识符”、“优先数”、“剩余运行时间”等，而不需要对系 统中真正的 PCB 等数据进行修改。首先建立一个就绪队列，随机生成信息建立若 干个进程；然后进行进程调度；将正在运行进程指针指向的进程控制块的内容以及调度一次 后进程队列的现状输出，查看结果。要求每个算法都需要将所有进程都执行结束。

以下是一个简单的单处理器系统中进程调度的示例代码，包括时间片轮转、优先数、最短进程优先和最短剩余时间优先四种调度算法。代码中使用了结构体来定义进程控制块（PCB），包括进程标识符、优先数、剩余运行时间和状态等信息。同时，代码中还实现了进程创建原语和进程调度原语，以及对就绪队列进行管理的相关函数。请注意，此代码仅供参考。

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

#define MAX_PROCESSES 10
#define TIME_QUANTUM 4

typedef enum {READY, RUNNING, TERMINATED} process_state;

typedef struct {
    int pid;
    int priority;
    int remaining_time;
    process_state state;
} pcb;

int num_processes;
pcb processes[MAX_PROCESSES];
int current_process = -1;

int get_random(int min, int max) {
    return rand() % (max - min + 1) + min;
}

pcb create_process(int pid) {
    pcb new_process;
    new_process.pid = pid;
    new_process.priority = get_random(1, 10);
    new_process.remaining_time = get_random(1, 10);
    new_process.state = READY;
    return new_process;
}

void init_processes() {
    for (int i = 0; i < num_processes; i++) {
        processes[i] = create_process(i);
    }
}

void print_processes() {
    for (int i = 0; i < num_processes; i++) {
        printf("Process %d: priority=%d, remaining_time=%d, state=%d\n", processes[i].pid, processes[i].priority, processes[i].remaining_time, processes[i].state);
    }
}

void schedule_time_slice() {
    if (current_process != -1) {
        processes[current_process].remaining_time -= TIME_QUANTUM;
        if (processes[current_process].remaining_time <= 0) {
            processes[current_process].state = TERMINATED;
            printf("Process %d terminated.\n", processes[current_process].pid);
            current_process = -1;
        }
        else {
            processes[current_process].state = READY;
            printf("Process %d time slice complete.\n", processes[current_process].pid);
        }
    }
}

void schedule_priority() {
    int highest_priority = -1;
    int highest_priority_process = -1;
    for (int i = 0; i < num_processes; i++) {
        if (processes[i].state == READY && processes[i].priority > highest_priority) {
            highest_priority = processes[i].priority;
            highest_priority_process = i;
        }
    }
    if (highest_priority_process != -1) {
        if (current_process != -1) {
            processes[current_process].state = READY;
        }
        current_process = highest_priority_process;
        processes[current_process].state = RUNNING;
        printf("Process %d selected by priority scheduling.\n", processes[current_process].pid);
    }
}

void schedule_shortest_job_first() {
    int shortest_time = -1;
    int shortest_time_process = -1;
    for (int i = 0; i < num_processes; i++) {
        if (processes[i].state == READY && (shortest_time == -1 || processes[i].remaining_time < shortest_time)) {
            shortest_time = processes[i].remaining_time;
            shortest_time_process = i;
        }
    }
    if (shortest_time_process != -1) {
        if (current_process != -1) {
            processes[current_process].state = READY;
        }
        current_process = shortest_time_process;
        processes[current_process].state = RUNNING;
        printf("Process %d selected by shortest job first scheduling.\n", processes[current_process].pid);
    }
}

void schedule_shortest_remaining_time_first() {
    int shortest_time = -1;
    int shortest_time_process = -1;
    for (int i = 0; i < num_processes; i++) {
        if (processes[i].state == READY && (shortest_time == -1 || processes[i].remaining_time < shortest_time)) {
            shortest_time = processes[i].remaining_time;
            shortest_time_process = i;
        }
    }
    if (shortest_time_process != -1) {
        if (current_process != -1) {
            processes[current_process].state = READY;
        }
        current_process = shortest_time_process;
        processes[current_process].state = RUNNING;
        printf("Process %d selected by shortest remaining time first scheduling.\n", processes[current_process].pid);
    }
}

void schedule_processes(int algorithm) {
    switch (algorithm) {
        case 1:
            schedule_time_slice();
            break;
        case 2:
            schedule_priority();
            break;
        case 3:
            schedule_shortest_job_first();
            break;
        case 4:
            schedule_shortest_remaining_time_first();
            break;
        default:
            printf("Invalid scheduling algorithm.\n");
    }
}

int all_processes_terminated() {
    for (int i = 0; i < num_processes; i++) {
        if (processes[i].state != TERMINATED) {
            return 0;
        }
    }
    return 1;
}

int main() {
    num_processes = get_random(1, MAX_PROCESSES);
    init_processes();
    printf("Initial process state:\n");
    print_processes();
    printf("Starting time slice scheduling:\n");
    while (!all_processes_terminated()) {
        schedule_processes(1);
        print_processes();
    }
    printf("Time slice scheduling complete.\n\n");
    current_process = -1;
    for (int i = 0; i < num_processes; i++) {
        processes[i].state = READY;
    }
    printf("Starting priority scheduling:\n");
    while (!all_processes_terminated()) {
        schedule_processes(2);
        print_processes();
    }
    printf("Priority scheduling complete.\n\n");
    current_process = -1;
    for (int i = 0; i < num_processes; i++) {
        processes[i].state = READY;
    }
    printf("Starting shortest job first scheduling:\n");
    while (!all_processes_terminated()) {
        schedule_processes(3);
        print_processes();
    }
    printf("Shortest job first scheduling complete.\n\n");
    current_process = -1;
    for (int i = 0; i < num_processes; i++) {
        processes[i].state = READY;
    }
    printf("Starting shortest remaining time first scheduling:\n");
    while (!all_processes_terminated()) {
        schedule_processes(4);
        print_processes();
    }
    printf("Shortest remaining time first scheduling complete.\n\n");
    return 0;
}