getchar() 实际上并没有从用户那里获取输入

我正在用C++编写一个灵活的命令行（但不会太长！）菱形方形生成器。我刚刚写完了用户输入的一半。然而，在最后一个命令中，输入"slips"，并自动向getchar（）输入一行换行符。我已经采取了预防措施，以确保它不会出现任何类型的溢出，即同时刷新stdin和stdout。问题仍然存在。这是我的代码：

#include <stdio.h>
#include <stdlib.h>
int main () {
    unsigned  long seed = 0, x = 0, y = 0, initial = 0, range = 0;
    int smooth = 0, fail = 1;
    char flagchar1 = 'n';
    printf("Welcome to my diamond-square generator! This isn't full-feature yet, so I'm just gonna have you input the variables one by one. ");
    do {
        printf("Please input the seed (this is a positive integer):n");
        fail = scanf("%lu", &seed);
        while (fail == 0) {
            printf("Try again, smartass.n");
            fail = scanf("%lu", &seed);
        }
        fail = 1;
        printf("Now input the x, or horizontal, size of your grid:n");
        fail = scanf("%lu", &x);
        while (fail == 0) {
            printf("An integer. Not a string. An integer. You can do that, can't you?n");
            fail = scanf("%lu", &x);
        }
        fail = 1;
        printf("Now input the y, or vertical, size of your grid:n");
        fail = scanf("%lu", &y);
        while (fail == 0) {
            printf("What was that supposed to be? An integer, please.n");
            fail = scanf("%lu", &y);
        }
        fail = 1;
        printf("Now input about how high you'd like the grid to be (this goes from a scale of 1 to 256):n");
        fail = scanf("%lu", &initial);
        while (initial == 0 || initial > 256 || fail == 0) {
            printf("ahahahahaha how HIGH do you have to be just to HAVE that hieght........n");
            fail = scanf("%lu", &initial);
        }
        fail = 1;
        printf("Now input the range of the heights on your grid (this must be equal to or less than 256):n");
        scanf("%lu", &range);
        while (range >= 256 || fail == 0) {
            printf("What did I say about being equal to or less than 256? Give me something reasonable to work with here.n");
            fail = scanf("%lu", &range);
        }
        fail = 1;
        printf("Just one more variable to go! Now, I need you to input the smoothness of your grid. Smaller numbers make spikier grids. You can make this negative, but beware!n");
        fail = scanf("%d", &smooth);
        while (fail == 0) {
            printf("That... was not a number.n");
            fail = scanf("%d", &smooth);
        }
        fail = 1;
        printf("nOkay. Are these the values you want?n   Seed:       %lun   Width:      %lun   Length:     %lun   Height:     %lun   Range:      %lun   Smoothness: %dnDo you want to keep these? Type Y/n.n", seed, x, y, initial, range, smooth);
        fflush(stdin);
        fflush(stdout);
        flagchar1 = getchar();
    } while (flagchar1 != 'y' && flagchar1 != 'Y' && flagchar1 != 'n');
}

这是我的输出，程序已经结束（如果我从while()中删除&& flagchar1 != 'n'，程序只重复整个do-while循环）：

欢迎使用我的菱形发电机！这还不是全部功能，所以我只是让你一个接一个地输入变量。请输入种子（这是一个正整数）：12345678现在输入网格的x或水平大小：40现在输入网格的y或垂直大小：30现在输入您希望网格的高度（从1到256）：1288哈哈哈哈，你必须有多高才能拥有它。。。。。。。。128现在输入网格上的高度范围（必须等于或小于256）：30还有一个变量！现在，我需要您输入网格的平滑度。数字越小，网格越尖。你可以说这是负面的，但要小心！10可以这些是你想要的价值观吗？种子：12345678宽度：40长度：30高度：128范围：30平滑度：10你想保留这些吗？类型Y/n。

发生了什么，我该如何解决？

附言：我知道我的输入验证基本上是无用的。我们也非常感谢您的帮助。