求助，为啥我的0删不掉

#include <bits/stdc++.h>
using namespace std;
#define int long long
string a;
signed main()
{
    cin>>a;
    if(a[0]=='-')
    reverse(a.begin()+1,a.end());
    else
    reverse(a.begin(),a.end());
    while(a[0]=='0')
      a.erase(0,1);
for(auto it: a)
    cout<<it;

}