这段代码是malloc函数和动态数组操作的练习，非常简单：程序必须为255个无符号字符分配255字节的内存（与普通整数的不同之处在于字符只占一个字节，所以当我不需要大于255的数字时，我保存了内存，这只是一个细节），然后它询问用户在写入0之前，他想对该数组做什么，现在的选项只有3.一个非常简单的练习，让我学习使用动态数组，但有一个问题，我不明白！当我分配内存一切顺利，直到执行扫描函数：在扫描变量“select”之后，数组指针变为NULL，我不知道为什么。这不可能是内存冲突问题，因为数组不会被存储。我该怎么办？
这里的代码，并提前感谢帮助：

#include <stdio.h>
#include <stdlib.h>
#define TRY
void main(){
    
    
    //the array is dinamically allocated in the heap memory and when it has a valid address the program starts
    unsigned char select = 1; //this variable is useful for the choice of the utent
    unsigned char length = 0; //this has no need to be explained
    unsigned char index = 0; //this variable can be used as temporary variable in the program
    unsigned char * array = (unsigned char*)malloc(255);
    if(array){
        
        while(select){
            #ifdef TRY
            printf("\t- - Array stored in %p memory address - -\n", array);
            #endif
            
            printf("What wanna do?\n1 - show array\n2 - insert value\n3 - edit value\n0 - quit\n");
            scanf("%d", &select);
            
            //generally the problems start from here: after the scanf the pointer turns into a NULL, you can see by the execution of the next line
            #ifdef TRY
            printf("\t- - Array stored in %p memory address - -\n", array);
            #endif
            switch(select){
                case 0: printf("Bye!\n");
                break;
                
                
                case 1: 
                    printf("Elements: %u\n", length);
                    for(index = 0; index < length; index++) printf("%d\t", *(array+index));
                break;
                
                
                case 2:
                    if(length<255){
                        
                        printf("Write the value to insert in the %p memory address: ", array+length);
                        scanf("%d", (array+length));
                        printf("Value %d added in %p address\n", *(array+length), array+length);
                        
                        length = length+1;
                    }
                    else 
                        printf("Array is full\n");
                break;
                
                
                case 3:
                    printf("Write the index value: ");
                    scanf("%d", &index);
                    if(index<length){
                        
                        printf("Write the value to insert in the %p memory address: ", array+index);
                        scanf("%d", array+index);
                        printf("Value %d written in %p address\n", *(array+length), array+length);
                        
                    }
                    else
                        printf("Invalid index\n");
                break;
                
                
                default: printf("Invalid input\n");
                break;
            }
        }
        free(array);
    }
    else printf("Memory error\n");
}

我还尝试用同样的malloc函数分配同一个数组中的其他变量，解释得更好，我创建了三个unsigned char指针而不是前三个unsigned char变量，并将数组最后三个字节的地址赋给它们，指针不再为NULL，但数组总是空的：在数组中插入一个值后，每次程序在“选择”时使用扫描函数，数组总是被清空。2问题总是相同的。