如何解决声明错误

我正在尝试运行一个代码，该代码需要用户输入的标准时间并将其转换为军事时间。对于用户输入，可以将小时键入一个或两个数字，并且可以以任何方式键入AM/PM。鉴于此，我拥有的代码如下：

#include <iostream>
#include <string>
using namespace std;
string time, hour, minute, amPm, miltime;
char amPmCheck;
int main()
{
    cout<<"Enter time:n";
    cin>>time;
    colon = time.find(':');
    space = time.find (' ');
    hour = time.substr(0, colon);
    minute = time.substr(colon + 1, space);
    amPm = time.substr(space, back);
    amPmCheck = amPm[0];
    timeConversion(hour, minute, amPmCheck);
    return 0;
}

void timeConversion(hour, minute, amPmCheck)
{
    if(amPmCheck == 'a'||'A')
    {
        if(int(hour) == 12)
        {
            hour.assign('00');
        }
        else if (int(hour) <= 9)
        {
            hour.insert(0, '0');
        }
    }
    else
        if(int(hour) < 12)
        {
            hour.assign(12+int(hour));
        }
    miltime = hour + minute
    cout<< "Corresponding military time is", miltime;
}

但是，在尝试编译代码时，我从所选编译器中获取以下错误：

main.cpp:50:25: warning: multi-character character constant [-Wmultichar]
             hour.assign('00');
                         ^~~~
main.cpp:15:8: error: 'std::string time' redeclared as different kind of symbol
 string time, hour, minute, amPm miltime;
        ^~~~
In file included from /usr/include/pthread.h:24:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/gthr-default.h:35,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/gthr.h:148,
                 from /usr/include/c++/6/ext/atomicity.h:35,
                 from /usr/include/c++/6/bits/ios_base.h:39,
                 from /usr/include/c++/6/ios:42,
                 from /usr/include/c++/6/ostream:38,
                 from /usr/include/c++/6/iostream:39,
                 from main.cpp:10:
/usr/include/time.h:192:15: note: previous declaration 'time_t time(time_t*)'
 extern time_t time (time_t *__timer) __THROW;
               ^~~~
main.cpp:44:21: error: variable or field 'timeConversion' declared void
 void timeConversion(hour, minute, amPmCheck)
                     ^~~~
main.cpp:44:35: error: 'amPmCheck' was not declared in this scope
 void timeConversion(hour, minute, amPmCheck)
                                   ^~~~~~~~~

我仍然对编程相对较新，因此，关于我的错误是什么以及最简单的解决方法的任何信息将不胜感激。