rand() 函數生成錯誤范圍內的數字

Question

我猜數字游戲有問題。 該程序由2部分組成。 在第一部分，用戶嘗試猜測計算機隨機生成的數字。 在第 2 部分，計算機嘗試估計用戶輸入的數字。 第 1 部分沒有問題，但在第 2 部分，計算機在進行預測時會估計不提供范圍的值。 所以，我在rand()函數中使用變量a和b創建了1到1000之間的數字，並定義為a = 1 b = 1000。計算機根據用戶的回答不斷縮小這個范圍。

例如，用戶輸入了數字649，如果計算機估計為800，則相關部分正在工作，並且b的新值是800，而不是1000，因此更新上限。 如果計算機估計為 200，則相關部分再次工作，a 的新值是 200，當循環回繞時，產生的是 200 到 800 之間的數字，而不是 1 到 1000 之間的數字。 但問題是即使值更新后，計算機生成一個大於 800 的數字（例如，1246）。 這正是問題所在。

我必須在星期二交付這項作業，但我仍然無法找到解決此錯誤的方法。 我正在向您發送源代碼，並詳細寫下了我使用的每個變量如何作為注釋編號。 如果需要，我可以發送錯誤的視頻描述。 請幫我。

為了幫助您更快地找到和測試問題，我禁用了一些帶有注釋行向用戶提問的行。

/*
                VARIABLES

    a=          rand() fonction min limit.
    b=          rand() fonction max limit.
    i=          attempts of user
    j=          attempts of computer
    rnd1=       The computer generated number that the user is trying to find.
    rnd2=       The number generated by the computer when estimating the number entered by the user and changing in each cycle.
    number2=    The number the computer is trying to find.
    number1=    Each number that the user enters when trying to find the number created by the computer.
    input=      The value that takes the answer to the questions the computer asks the user.
    restart=    The value that is defined to 1 and allows the game to restart unless the user changes the value.

    ATTENTION:  In order to help you find and test the problem faster, I disabled some 
                lines where the user was asked questions with a comment line.
*/

#include "stdlib.h"
#include <stdio.h>
#include <dos.h>
#include <windows.h>
#include <locale.h>

int main()
{
    int i, j = 1, rnd1, rnd2, number2 = 0, number1 = 0, b = 1000, a = 1, input, restart = 1;

    setlocale(LC_ALL, "Turkish");       

    do
    {
        printf("\t\t\t\t-----------------------------------------\n");
        printf("\t\t\t\t|                    |\n");
        printf("\t\t\t\t|      Welcome to Guess Number Game      |\n");         
        printf("\t\t\t\t|                    |\n");
        printf("\t\t\t\t-----------------------------------------\n");

        printf("Game is starting...\n");
        printf("3\n");
        Sleep(1000);
        printf("2\n");
        Sleep(1000);            
        printf("1");
        Sleep(1000);
        system("cls");

        srand(time(NULL));
        rnd1 = a + rand() % b;      

        printf("Computer: Let's try to guess the number that in my mind :)\n\n");
        for (i = 1; number1 != rnd1; i++)
        {
            printf("Computer: What is your guess?\n");
            printf("Number: ");                 
            scanf_s("%d", &number1);
            printf("\n");

            if (number1 < rnd1)
            {
                printf("Computer: The secret number is greater than your guess. Try again...\n");
            }
            else if (number1 > rnd1)
            {
                printf("Computer: The secret number is smaller than your guess. Try again...\n");
            }
            else
            {
                printf("Computer: Congratulations!!!  You know the number at your %d’th guess\n\n\n", i);
                printf("\t\t\t\t------------------------------------------\n");
                printf("\t\t\t\t|                     |\n");
                printf("\t\t\t\t|           Computer's Turn...        |\n");
                printf("\t\t\t\t|                     |\n");
                printf("\t\t\t\t------------------------------------------\n");

                printf("3\n");
                Sleep(1000);
                printf("2\n");
                Sleep(1000);            
                printf("1");
                Sleep(1000);
                system("cls");
            }
        }
        printf("Computer: Now, its my turn. Write a number and I'll try to find it...\n");
        printf("Number: ");
        scanf_s("%d", &number2);
        printf("\n");

        while (j != -1)
        {
            rnd2 = a + rand() % b;
            if (rnd2 == number2)
            {
                printf("Computer: My guess is %d. Is this true ?\n", rnd2);
                //printf("1)Yes. It is equal to the number which is in my mind.\n");
                //printf("2)No. It is greater than to the number which is in my mind.\nNumber: ");
                //printf("2)No. It is smaller than to the number which is in my mind.\nNumber: ");
                //scanf_s("%d", &input);
                //printf("\n\n");
                //if (input == 1)
                //{
                //  printf("Computer: I found! I found!. The secret number is %d.\n\n", rnd2);
                //}
                //else if (input == 2)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's true :)\n");
                //}
                //else if (input == 3)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's true :)\n");
                //}
                break;
            }
            else if (rnd2 < number2)
            {
                printf("Computer: My guess is %d. Is this true ?\n", rnd2);
                //printf("1)Yes. It is equal to the number which is in my mind.\n");
                //printf("2)No. It is greater than to the number which is in my mind.\nNumber: ");
                //printf("2)No. It is smaller than to the number which is in my mind.\nNumber: ");
                //scanf_s("%d", &input);
                //printf("\n\n");
                //if (input == 1)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's smaller than yours :)\n");
                //}
                //else if (input == 2)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's smaller than yours :)\n");
                //}
                //else if (input == 3)
                //{

                //}
                a == rnd2;
            }
            else if(rnd2>number2)
            {
                printf("Computer: My guess is %d. Is this true ?\n", rnd2);
                //printf("1)Yes. It is equal to the number which is in my mind.\n");
                //printf("2)No. It is greater than to the number which is in my mind.\nNumber: ");
                //printf("2)No. It is smaller than to the number which is in my mind.\nNumber: ");
                //scanf_s("%d", &input);
                //printf("\n\n");
                //if (input == 1)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's greater than yours :)\n");
                //}
                //else if (input == 2)
                //{

                //}
                //else if (input == 3)
                //{
                //  printf("Don't try to fool me, I'm a computer. I know it's greater than yours :)\n");
                //}
                b == rnd2;
            }
            j++;
        }

        if (i < j)
        {
            printf("Game is ending...\n");
            printf("3\n");
            Sleep(1000);
            printf("2\n");
            Sleep(1000);                            //
            printf("1");                        
            Sleep(1000);
            system("cls");

            printf("\t\t\t\t------------------------------------------\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t|  You are the winner. CONGRATULATIONS.  |\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t------------------------------------------\n");
            printf("You know the number at your %d’th guess\n", i);
            printf("Computer know the number at %d’th guess\n\n", j);
            printf("Do you want to play again?\n");
            printf("1)Yes\n");
            printf("2)No\nSelection:");
            scanf_s("%d", &restart);

        }
        else if (i > j)
        {
            printf("Game is ending...\n");
            printf("3\n");
            Sleep(1000);
            printf("2\n");
            Sleep(1000);            //Game end countdown.
            printf("1");
            Sleep(1000);
            system("cls");
            printf("\t\t\t\t-----------------------------------------\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t|      Computer is the winner. You lose.     |\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t-----------------------------------------\n");
            printf("You know the number at your %d’th guess\n", i);
            printf("Computer know the number at %d’th guess\n\n", j);
            printf("Do you want to play again?\n");
            printf("1)Yes\n");
            printf("2)No\nSelection:");
            scanf_s("%d", &restart);
        }
        else
        {
            printf("Game is ending...\n");
            printf("3\n");
            Sleep(1000);
            printf("2\n");
            Sleep(1000);            //Game end countdown.
            printf("1");
            Sleep(1000);
            system("cls");
            printf("\t\t\t\t-----------------------------------------\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t|      Your match ended in a draw. Do you want to play again?    |\n");
            printf("\t\t\t\t|                    |\n");
            printf("\t\t\t\t-----------------------------------------\n");
            printf("You know the number at your %d’th guess\n", i);
            printf("Computer know the number at %d’th guess\n\n", j);
            printf("Do you want to play again?\n");
            printf("1)Yes\n");
            printf("2)No\nSelection:");
            scanf_s("%d", &restart);
        }
    } while (restart == 1);

    system("PAUSE");
    return 0;
}

Answer 1

在a + rand() % b; , rand() % b結果是從 0 到b -1（含）的數字。 然后加上a會產生一個從a到a + b -1 的數字，包括。 所以，如果a是 200， b是 800，它會產生一個從 200 到 200+800−1 = 999（含）的數。

要生成從a到b （含），請使用a + rand() % (b+1-a) 。 或者，要排除b ，請使用a + rand() % (ba) 。

注意：

(a) 隨機使用%會使分布偏向低值。 這是因為rand產生的數字范圍（0 到RAND_MAX ，包括）通常不能被b整除，所以有一些剩余片段，使用%將這個片段中的所有數字放在分布的低端。

(b) rand歷史實現因低位的低熵而臭名昭著，因此，只要b是 2 的冪的倍數，例如 2 ⁿ ， n低位就不是很隨機。

出於這些原因，以這種方式將%與rand一起使用不應在簡單的課堂練習和其他隨意使用之外進行。