原文链接：https://blog.csdn.net/qq_39355828/article/details/116008026 (opens new window)

递归产生回文数

回文数 包括小写字母的随机产生，大写字母的随机产生，首先显示一个菜单，然后选中需要产生的回文数市数字，小写英文，还是大写英文，进而输入产生的回文数的长度。

// Program RollDice.cpp
// This program demonstrates using random numbers
// to simulate rolling dice.

#include <iostream>
#include <cstdlib>   // rand and srand
#include <ctime>     // For the time function
using namespace std;
void Intfunc(int n);
void showMenu();
void Upperfunc(int n);
void Intfunc1(int n);
void Upperfunc1(int n);
void Lowerfunc1(int n);
void Lowerfunc(int n);
void delay_sec(int sec);
int main()
{  int length,choice;
   int ADULT_CHOICE=1;
   int QUIT_CHOICE=4;
   int m;
   do
   {
      // Display the menu and get the user's choice.
      showMenu();
      cin >> choice;

      // Validate the menu selection.
      while (choice < ADULT_CHOICE || choice > QUIT_CHOICE)
      {  cout<<choice;
         cout << "is not a valid choice!\n";
         cout<<  "Please enter a number from 1 to 4.\n";
         cout<<"Your choice?";
         cin >> choice;
      }

      // If the user does not want to quit, proceed.
      if (choice != QUIT_CHOICE)
      {   cout<<"How long would you like your palindrome to be?";
          cin>>length;
          while (length < 0)
        {

         cout<<  "Please enter a length grater than 0!\n";
         cout<<"Your length?";
         cin >> length;
        }
          cout<<"\nGenerating your palindrome...\n";
          if(choice==1)
          {
          	  if(length%2==1)
               {
                 m=length/2+1;
                 Intfunc1(m);
			   }
               if(length%2==0)
                {
                m=length/2;
                Intfunc(m);
				}
		  }
		   if(choice==2)
          {
          	  if(length%2==1)
               {
                 m=length/2+1;
                 Upperfunc(m);
			   }
               if(length%2==0)
                {
                m=length/2;
                Upperfunc1(m);
				}
		  }
		   if(choice==3)
          {
          	  if(length%2==1)
               {
                 m=length/2+1;
                 Lowerfunc(m);
			   }
               if(length%2==0)
                {
                m=length/2;
                Lowerfunc1(m);
				}
		  }

      }
   } while (choice != QUIT_CHOICE);
   cout<<"Thanks for using my palindrome generator!!"<<endl;
   cout<<"Come back soon!"<<endl;

   return 0;

}
void showMenu()
{  cout<<"\n------------------------------------"<<endl;
   cout << "Welcome to the palindrome generate!\n\n"
        <<"------------------------------------\n"
        <<"Choose the type of palindrome you'd like to generate\n"
        <<"from the menu below,or choose 4 to qiut the program.\n"
        << "1) Digits\n"
        << "2) Uppercase letters\n"
        << "3) Lowercase letters\n"
		<<"4) Quite program\n"
		<<"\n------------------------------------\n"
        << "Your choice?  ";
}
void Intfunc(int n)//even number
{
	unsigned int seed = (unsigned int)(time(0));

   // Seed the random number generator.
   srand(seed);

   // Get some die values.
   int value = rand() % 9 + 1;
   //Sleep(1000);
   delay_sec(5);
   if(n==1)
   {
   	printf("%d",value);
   	printf("%d",value);
   }
   else
   {
   	  printf("%d",value);
   	  Intfunc(n-1);
   	  printf("%d",value);
   }
}
void Intfunc1(int n)//odd number
{
	unsigned int seed = (unsigned int)(time(0));

   // Seed the random number generator.
   srand(seed);

   // Get some die values.
   int value = rand() % 9 + 1;
delay_sec(5);
   if(n==1)

   printf("%d",value);

   else
   {
   	  printf("%d",value);
   	  Intfunc1(n-1);
   	  printf("%d",value);
   }
}
void Upperfunc(int n)//A B C odd number
{
	unsigned int seed = (unsigned int)(time(0));
    int MAX_VALUE=90;
    int MIN_VALUE=65;
   // Seed the random number generator.
   srand(seed);
   int value= (rand() % (MAX_VALUE - MIN_VALUE + 1)) + MIN_VALUE;
   // Get some die values.
   //int value = rand() % 9 + 1;
   delay_sec(5);
   if(n==1)
   printf("%c",value);
   else
   {
   	  printf("%c",value);
   	  Upperfunc(n-1);
   	  printf("%c",value);
   }
}
void Upperfunc1(int n)//A B C even number
{
	unsigned int seed = (unsigned int)(time(0));
    int MAX_VALUE=90;
    int MIN_VALUE=65;
   // Seed the random number generator.
   srand(seed);
   int value= (rand() % (MAX_VALUE - MIN_VALUE + 1)) + MIN_VALUE;
   // Get some die values.
   //int value = rand() % 9 + 1;
   delay_sec(5);
   if(n==1)
   {
   	printf("%c",value);
   	printf("%c",value);
   }
   else
   {
   	  printf("%c",value);
   	  Upperfunc1(n-1);
   	  printf("%c",value);
   }
}
void Lowerfunc(int n)//odd number
{
	unsigned int seed = (unsigned int)(time(0));
    int MAX_VALUE=122;
    int MIN_VALUE=97;
   // Seed the random number generator.
   srand(seed);
   int value= (rand() % (MAX_VALUE - MIN_VALUE + 1)) + MIN_VALUE;
   // Get some die values.
   //int value = rand() % 9 + 1;
   delay_sec(5);
   if(n==1)
   printf("%c",value);
   else
   {
   	  printf("%c",value);
   	  Lowerfunc(n-1);
   	  printf("%c",value);
   }
}
void Lowerfunc1(int n)//even number
{
	unsigned int seed = (unsigned int)(time(0));
    int MAX_VALUE=122;
    int MIN_VALUE=97;
   // Seed the random number generator.
   srand(seed);
   int value= (rand() % (MAX_VALUE - MIN_VALUE + 1)) + MIN_VALUE;
   // Get some die values.
   //int value = rand() % 9 + 1;
   delay_sec(5);
   if(n==1)
   {
   	printf("%c",value);
   	printf("%c",value);
   }
   else
   {
   	  printf("%c",value);
   	  Lowerfunc1(n-1);
   	  printf("%c",value);
   }
}

void delay_msec(int msec)
{
 clock_t now = clock();
 while(clock()-now < msec);
}

void delay_sec(int sec)//
{
 time_t start_time, cur_time;
 time(&start_time);
 do
 {
  time(&cur_time);
 } while((cur_time - start_time) < sec);
}

需要注意：随机数的产生和系统的时间有关系，随机数时间如果相邻太短，则相对的时间太少，产生的随机数可能会一致，因此考虑使用延时函数