c++ srand(time(0)) 在猜谜游戏中不起作用

Question

I need to make a guessing game in C++, and everything works except that srand(time(0)) doesn't reset the number after the user wants to play again. I also can't use std libraries.

Nothing I have done has worked so far. Am I doing the while loops wrong?

#include <iostream>
#include <ctime>
using namespace std;

int main()
{
  //Initialize variables
  int input = 0;
  int playing = 1;
  char yninput[2];
  int count = 1;
  //While the player is playing the game
  while (playing == 1) {
    srand(time(0));
    int num = rand() % 101;
    //While the player hasn't guessed the number
    while (input != num) {
     //Prompt the player
       cout << "Enter your guess" << endl;
      cout << num << endl;
      cin >> input;
      //If the guess is greater than the number
      if (input > num) {
    cout << " Your guess is too high!" << endl;
   count++;
      } 
      //If the guess is less than the number
      else if (input < num) {
    cout << " Your guess is too low!" << endl;
    count++;
      }
      //If the player guesses the correct number
      else {
    cout << " You have guessed the number! It took you " << count << " 
guess(es)! Would you like to play again?" << endl;
    //Ask the play if they want to play again
    cin >> yninput[2];
    //If the player doesn't want to play again quit the program
    if (yninput[2] == 'n') {
      playing = 0;
      input = num;
        }
    //If the player wants to play again restart the program and 
     randomize the number
    else if (yninput[2] == 'y') {
       input = 0;
      count = 1;
         }
      }
    }
  }
}

Answer 1

As @user4581301 has pointed out, you shouldn't call srand(time(0)) more than once, as it will reset the random seed according to the current system time. If srand(time(0)) is called in rapid succession, the very big number that it will take as a seed (which I believe is the current epoch time ) will be sufficiently close to the previous call that you might not observe significant difference in your RNG.

Simply moving the srand(time(0)); line out of the while loop should do the trick.

Answer 2

How do I get it so that when the user presses 'y' and the game resets that the random number also changes?

You get the next number in the pseudo random sequence by calling rand without calling srand in between. If you set the random sequence to start from the current timestamp on every iteration, then you get the same number which changes once a second.

I also can't use std libraries.

srand, rand, time, cout and cin are all from the standard library.

Answer 3

I think @Mathis has already pointed out the solution.

I am just sharing some insight as to how srand and rand are related. Consider the below code snippet:

#include <iostream>
#include <ctime>
int main()
{
    int i = 0;
    // Uncomment below line to generate new set of random numbers
    // on every execution.
    // srand(time(0));   
    while (i < 5)
    {
        std::cout<< rand() % 10 <<std::endl;
    }
}

Let's say the program generates numbers - 5, 7, 3, 0 and 4 on 1st run. If you run the program again, you will see the same set of numbers, ie, 5, 7, 3, 0 and 4. So, although they are random (pseudo random to be precise), but on every program execution, the order of numbers will be same.

This is the reason we use srand to specify some seed value. Seed is any value which is different on each execution. When we use time(0) as parameter to srand , we make sure that on every program execution, we are providing a new and unique seed. This will make sure that we get truly random set of numbers.