NOI / 1.5 Cycle control of programming basis 25: Find a special natural number

describe

• A decimal natural number , Its seven and nine decimal representations are three digits , And the order of the three digit numbers of the seventh and ninth system is just the opposite . Program to find this natural number , And output the display .

Input

• nothing .

Output

• Three elements ：
  The first line is the decimal representation of this natural number ;
  The second line is the hexadecimal representation of this natural number ;
  The third line is the hexadecimal representation of this natural number .
• ac Code

#include<iostream> 
#include<cmath>
using namespace std;
int seventoten(int n){
    
   int r=0,i=0,t;
   while(n){
    
   	t=n%10;
   	n/=10;
   	r+=t*pow(7,i);
   	i++;	
   } 
   return r;
}
int reverse(int n){
    
   int r=0,i=0,t=n,mask=1;
   while(t>9){
    
   	t/=10;
   	mask*=10;
   }
   while(n){
    
   	t=n%10;
   	r+=t*mask;
   	mask/=10;
   	n/=10;
   } 
   return r;
}
int tentonine(int n){
    
   int r=0,t,i=1;
   while(n){
    
   	t=n%9;
   	r+=t*i;
   	i*=10;
   	n/=9;
   }
   return r;
}
int tentoseven(int n){
    
   int r=0,t,i=1;
   while(n){
    
   	t=n%7;
   	r+=t*i;
   	i*=10;
   	n/=7;
   }
   return r;
}
int main()
{
    
   int h,i,j;
   for(h=100;h<1000;h++){
    
   	i=tentoseven(h);
   	j=tentonine(h);
   	if(i==reverse(j)){
    
   		cout<<h<<endl;
   		cout<<i<<endl;
   		cout<<j<<endl;
   		break;
   	}
   }
}

Ideas

• Two binary conversion functions , One reverse function
• There is a loophole ： How to determine the range when retrieving from decimal numbers ？ How to make sure it's three digits , Here's the loop 100 It's a magic number

If you have better ideas and suggestions, please leave a message to me in the comment area. Thank you for your visit ！