C语言，代码中的一段导致无限循环

Question

写题时，代码中的一个 while 语句里出现了无限循环
当输入一个非数字如“fifty”时，while 中的 scanf 还没有输入，就一直出现“The Target weight: Error!”
应该是哪里出错了呢

---

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

int main()
{
    double w;          // input the target weight
    int check;         // check the return value of scanf
    char c;
    printf("Enter the Target Weight in lbs: ");
    check = scanf("%lf%c", &w, &c);


    // represent weight by available disks -- handle incorrect input
    double dec;                   // dec is the decimals part of w
    int check1, mark=0;           // check1 is a mark used to check if w is a pure number

    while (1)
    {
        if (check == 0 || !isspace(c)){         // Incorret: input is not a pure number
            check1 = 0;
        }
        else {                    // Incorrect: input can't be represented by available disks
            check1 = 1;
            dec = w-(int)w;
            if (dec==0.25 || dec==0.5 || dec==0.75 || dec==0){  
                mark=1;
            }
            else{
                mark=0;
            }
        }
        
        if (check1==0 || w<=0 || w>10000 || mark==0){
            printf("Error!\n");
            printf("The Target Weight: ");
            check = scanf("%lf%c", &w, &c);
        }
        else {
        ;
        }
    }
    return 0;
}

Answer 1

37行前面增加
getchar();