？

言归正传，N转M进制有问题，各位大佬能帮我看看吗？球球啦！

#include <bits/stdc++.h>

using namespace std;

long long fat10(long long x,long long y){

long long sum=1;

for(int i=1; i<=y; i++){

		sum*=x;

}

return sum;

}

string f10tb(long long x,long long y){

string s;

if(y<=9){

if(x==0) return "0";

while(x){

			s+=x%y+48;

            x/=y;
            
            }
            
	reverse(s.begin(),s.end());

	return s;

}

else{

	if(x==0) return "0";

	while(x){

		if(x%y>9){
  
			s+=x%y+55;
    
		}
  
		else{
  
			s+=x%y+48;
    
		}
  
		x/=y;
  
	}

	reverse(s.begin(),s.end());

	return s;

}

}

int main(){

string s;

int a,b;

cin>>s>>a>>b;

long long sum=0,cnt=0;

for(int i=s.size()-1; i>=0; i--){

	if(b>9){
  
		if(s[i]>'9') s[i]-=55;
    
		else s[i]-=48;
    
		sum+=s[i]*fat10(a,cnt);
    
		cnt++; 
  
	}

	else{

		s[i]-=48;
  
		sum+=s[i]*fat10(a,cnt);
  
		cnt++; 
  
	}

}

string s1=f10tb(sum,b);

for(int i=0; i<=s1.size()-1; i++){

	if(s1[i]>='A' and s1[i]<='Z'){

		s1[i]+=32;
  
	}

}

cout<<s1;

return 0;

}