C++高精度减法

#include <iostream>  
#include <vector>  
using namespace std;  
//高精度减法  
//判断A, B大小  
bool cmp(vector<int> A,vector<int> B){  
if(A.size() != B.size()) return A.size() > B.size();  
for(int i = 0;i < A.size();i++){  
if(A[i] != B[i]) return A[i] > B[i];  
}  
return true;  
}  
vector<int> sub(vector<int> A,vector<int> B){  
vector<int> C;  
for(int i = 0,t = 0;i < A.size();i++){  
// C[i] = A[i] - B[i] - t  
t = A[i] - t;  
if(i < B.size()) t -= B[i];  
  
C.push_back((t + 10) % 10);  
// 判断是否有借位  
if(t < 0) t = 1;  
else t = 0;  
}  
// 去掉前导0  
while(C.size() > 0 && C.back() == 0){  
C.pop_back();  
}  
return C;  
}  
int main(){  
string x,y;  
cin >> x >> y;  
vector<int> A,B;  
for(int i = x.size() - 1;i >= 0;i--) A.push_back(x[i] - '0');  
for(int i = y.size() - 1;i >= 0;i--) B.push_back(y[i] - '0');  
vector<int> C;  
// A >= B  
if(cmp(A,B)) C = sub(A,B);  
// A < B  
else {  
cout << '-';  
C = sub(B,A);  
}  
for(int i = C.size()-1;i >=0;i--) cout << C[i];  
  
}