c++string不懂为什么输入123会输出132231

#include<cstdio>
#include<algorithm>
#include<cstdlib>
#include<string>
#include<iostream>
using namespace std;
int main()
{
    string s;
    cin>>s;
    if(s[0]=='-'&&s[s.length()-1]!='0');
    {
        reverse(s.begin()+1,s.end());
        cout<<s;
    }
    if(s[0]=='-'&&s[s.length()-1]=='0')
    {
        reverse(s.begin()+1,s.end());
        s.erase(1);
        cout<<s;
    }
    if(s[0]!='-'&&s[s.length()-1]=='0')
    {
        reverse(s.begin(),s.end());
        s.erase(0);
        cout<<s;
    }
    if(s[0]!='-'&&s[s.length()-1]!='0')
    {
        reverse(s.begin(),s.end());
        cout<<s;
    }
    return 0;
}

输入123 输出132231

输入-120 输出-021

求大佬解惑555