<span style="font-size:24px;">int a[20] = {0};//定義一個數組
    for (int i = 0; i < 20; i++) {
        a[i] = arc4random() % (9999 - 1000 + 1) + 1000;
    }//為陣列a隨機賦值
    for (int i = 0; i < 20 - 1; i++) {
        for (int j = 0; j < 20 - 1 - i; j++) {
            if ((a[j] % 1000) > (a[j + 1] % 1000)) {
                int temp = a[j];
                a[j] = a[j + 1];
                a[j + 1] = temp;
            }
        }
    }//把陣列a進行升序排序
    for (int i = 0; i < 20; i++) {
        printf("%d ",a[i]);
    }
    printf("\n");
    int b[10] = {0};//定義一個數組b
    for (int i = 0; i < 10; i++) {
        b[i] = a[i];//把a中的前10個元素賦給b
    }
    for (int i = 0; i < 10; i++) {
        printf("%d ", b[i]);
    }
    printf("\n");
    int count = 0;//儲存b中後三位相等的數的個數
    for (int i = 0; i < 10; i++) {
        for (int j = 0; j < 10; j++) {
            if ((b[i] % 1000) == (b[i + j] % 1000)) {
                count++;
            }
            for (int k = i; k < i + count - 1; k++) {
                for (int m = i; m < i + count - 1; m++) {
                    if (b[m] < b[m+1]) {
                        int temp = b[m];
                        b[m] = b[m + 1];
                        b[m + 1] = temp;//把b中後三位相等的數進行排序
                    }
                }
            }
        }
        count = 0;//當b中後三位相等的數排完序後count置為0,記錄下一組後三位相等的數的個數
    }
    for (int i = 0; i < 10; i++) {
        printf("%d ", b[i]);
    }</span>
</span></span>