在可变分区管理方式下采用最先适应算法实现主存分配与回收代码实例

以下是采用最先适应算法实现主存分配与回收的代码实例：

#include<stdio.h>

int memory[50], n, choice, process_size, process_no;

void allocate(){
    int i, start_address, flag = 0;
    printf("\nEnter the process size: ");
    scanf("%d", &process_size);
    for(i = 0; i < n; i++){
        if(memory[i] == 0){
            start_address = i;
            while(memory[i] == 0 && i < n && (i-start_address+1) < process_size)
                i++;
            if((i-start_address+1) == process_size){
                process_no++;
                printf("\nProcess %d allocated from %d to %d.", process_no, start_address, i);
                for(int j = start_address; j <= i; j++)
                    memory[j] = process_no;
                flag = 1;
                break;
            }
        }
    }
    if(flag == 0)
        printf("\nMemory is full. Cannot allocate process.");
}

void deallocate(){
    int i, process_number;
    printf("\nEnter the process number to deallocate: ");
    scanf("%d", &process_number);
    for(i = 0; i < n; i++){
        if(memory[i] == process_number)
            memory[i] = 0;
    }
    printf("\nProcess %d deallocated successfully.", process_number);
}

void display(){
    printf("\nMemory status:\n");
    for(int i = 0; i < n; i++){
        if(memory[i] == 0)
            printf("%d\tFree\n", i);
        else
            printf("%d\tProcess %d\n", i, memory[i]);
    }
}

int main(){
    int i;
    printf("Enter the number of memory blocks: ");
    scanf("%d", &n);
    while(1){
        printf("\n1. Allocate a process\n2. Deallocate a process\n3. Display memory status\n4. Exit\nEnter your choice: ");
        scanf("%d", &choice);
        switch(choice){
            case 1: allocate(); break;
            case 2: deallocate(); break;
            case 3: display(); break;
            case 4: return 0;
            default: printf("\nInvalid choice.");
        }
    }
    return 0;
}

在这个代码实例中，我们定义了一个大小为50的数组 `memory` 来模拟主存储器的分区情况。当用户选择分配一个进程时，程序会遍历整个数组，找到第一个空闲分区，并检查该分区是否足够容纳进程，如果是，则按照进程大小将该分区分配给进程。当用户选择释放一个进程时，程序会遍历整个数组，找到该进程占用的分区，并将这些分区释放。当用户选择显示内存状态时，程序会遍历整个数组，显示每个分区的状态（空闲或被哪个进程占用）。