机试笔记3--进制转换

1.求反序数

#include  <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int ans = 0;
    while(n>0){
       ans = ans*10+n%10;
       n/=10;
    }  
    return 0;
}

2.十进制转x进制

#include <iostream>
#include <vector>
using namespace std;
/*通用版*/
int main()
{
    int num,x;
    cin >> num>>x;
    vector<char> bin;
    while(num>0){
      int w = num%x;
      if(w<10) bin.push_back(w+'0');
      else bin.push_back(w-10+'A');
      num/=x;
    }
    for(int i=bin.size()-1;i>=0;i--){
      cout << bin[i];
    }
    cout << endl;
   return 0;
}

3.X进制转10进制

#include <iostream>
#include <vector>
#include <math.h>
using namespace std;

int main()
{
   string n;
   int x;//输入数据和该数的进制
   cin >> n >> x;
   int len = n.size();
   int sum_m = 0;
   int j=0;
   for(int i=len-1;i>=0;i--){
     int p = pow(x,j);
     if('A'<=n[i]&&n[i]<='Z'){
       sum_m+=(n[i]-'A'+10)*p;
     }else{
       sum_m+=(n[i]-'0')*p;
      }
     j++;
   }
   cout << sum_m<<endl;
   return 0;
}

4.M进制转N进制

  先转成10进制，再转成N进制

#include <iostream>
#include <vector>
#include <math.h>
using namespace std;
//M进制转10进制
int mToten(string n,int x)
{
   int len = n.size();
   int sum_m = 0;
   int j=0;
   for(int i=len-1;i>=0;i--){
     int p = pow(x,j);
     if('A'<=n[i]&&n[i]<='Z'){
       sum_m+=(n[i]-'A'+10)*p;
     }else{
       sum_m+=(n[i]-'0')*p;
      }
     j++;
   }
   return sum_m;
}
//10进制转N进制
string tenTon(int n,int x)
{   string a;
    string ans;
    while(n>0){
      int w = n%x;
      if(w>9){
        a+=(w-10)+'a';
      }
      else a+=(w+'0');
      n/=x;
    }
    for(int i=(a.size()-1);i>=0;i--)
        ans+=a[i];
    return ans;
}

int main()
{
    int M,N;
    string x;
    cin >> M >> N;
    cin >> x;
    int num = mToten(x,M);
    string str = tenTon(num,N);
    cout << str;
    return 0;
}