unsigned long *primes=NULL;
    unsigned long trial =0;
   
    bool found = false;
    size_t total =0;
    size_t count =0;
   
    printf("........");
    scanf("%u",&total);
    total=total<4U ? 4U:total;
   
    primes=(unsigned long *)malloc(total*sizeof(unsigned long));
    if(primes==NULL)
    {
        printf("\n指向错误\n");
        return 1;
    }
   
    *primes =2UL;
    *(primes+1)=3UL;
    *(primes+2)=5UL;
    count =3U;
    trial =5U;

请大侠帮我看看这个4U,2UL,3UL,5UL, 3U,5U是啥?我照着书本抄的  就是看不明白这个

5U表示无符号常量5
5UL表示无符号长整型常量5