C++ How to loop this thing (beginner) - c++

Question

I'm figuring out how to loop my code and now it got me confused, any help would be much appreciated, im a beginner here so please don't scold me.
#include <iostream>
#include <string>
using namespace std;
int main()
{
string str;
char ans;
cout << "CONVERSION\n\n";
cout << "Base 11 to Decimal\n";
a:cout << "Base 11: ";
getline(std::cin, str);
const auto bad_loc = str.find_first_not_of("0123456789aA");
if (bad_loc != std::string::npos)
{
std::cerr << "Invalid Input\n";
goto a;
}
unsigned long ul = std::stoul(str, nullptr, 11);
cout << "Decimal: " << ul << "\n\n";
cout << "Do you want to continue (Y/N)? ";
cin >> ans;
if (ans == 'y')
{
goto a;
}
else if (ans == 'n')
{
cout <<"Name:\tXXXXXXXX\n";
cout <<"Course:\tXXXXXXXX";
cout <<"Section:\tXXXXXXXX\n";
cout <<"Schedule:\tXXXXXXXX\n";
cout <<"Professor:\tXXXXXXXX\n";
}
return 0;
}
the output should be like this
CONVERSION
Base 11 to Decimal
Base 11: B
Invalid Input!
Base 11: A
//blank
Do you want to continue (Y/N)? X
Invalid Answer! (Y/N)? Y
//blank
Base11:
My problems are
(1)The program stops after looping in "base11:" whenever i answer Y and (2)if I answer any letter from "Do you want..." the program will end. (3) How to fix this thing.

Answer 1

We beginners should help each other should not we?:)
The program can look something like the following
#include <iostream>
#include <string>
#include <limits>
int main()
{
std::cout << "CONVERSION\n\n";
std::cout << "Base 11 to Decimal\n";
char ans;
do
{
std::string s;
bool valid_input = false;
while ( !valid_input )
{
std::cout << "Base 11: ";
if ( !std::getline( std::cin, s ) ) break;
if ( !( valid_input = s.find_first_not_of( "0123456789aA" ) == std::string::npos ) )
{
std::cout << "Invalid Input\n\n";
}
}
if ( !valid_input )
{
std::cout << "See you later!" << std::endl;
break;
}
unsigned long value = std::stoul( s, nullptr, 11 );
std::cout << "Decimal: " << value << "\n\n";
std::cout << "Do you want to continue (Y/N)? ";
std::cin >> ans;
std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
} while ( ans == 'y' || ans == 'Y' );
std::cout <<"Name:\tXXXXXXXX\n";
std::cout <<"Course:\tXXXXXXXX";
std::cout <<"Section:\tXXXXXXXX\n";
std::cout <<"Schedule:\tXXXXXXXX\n";
std::cout <<"Professor:\tXXXXXXXX\n";
return 0;
}
If the input looks like
B
A
Y
C
AA
N
then the output will be
CONVERSION
Base 11 to Decimal
Base 11: B
Invalid Input
Base 11: A
Decimal: 10
Do you want to continue (Y/N)? Y
Base 11: C
Invalid Input
Base 11: AA
Decimal: 120
Do you want to continue (Y/N)? N
Name: XXXXXXXX
Course: XXXXXXXXSection: XXXXXXXX
Schedule: XXXXXXXX
Professor: XXXXXXXX
Pay attention to statement
std::cin.ignore( std::numeric_limits<std::streamsize>::max(), '\n' );
that skips the new line character entered after inputting ans using operator >>.

Answer 2

bool run_attempt() {
get some input
if (bad input)
return false;
else {
do something good with the input
return true;
}
}
void main() {
bool success = false;
while (!success) {
success = run_attempt();
}
}