Having problem validating the radius in this code - c++

Question

I have the following code in which I'm trying to validate the radius. If the radius is zero or negative, I'm supposed to give the user endless opportunities to write the radius again until it's valid. When I tested the code, I wrote a negative value and it worked just fine, it gave me endless opportunities until I gave a valid value, but if I wrote a correct value since the beginning, it made me write the value again as if it was incorrect.
#include <iostream>
#include <stdlib.h>
#include "listaEnlazada.h"
using namespace std;
using namespace listaenlazada;
void menu()
{
cout << "\n\t\tLISTA ENLAZADA SIMPLE\n\n";
cout << "1. Insert at begginig " << endl;
cout << "2. Insert at the end " << endl;
cout << "3. Insert in a specific position " << endl;
cout << "4. Write list " << endl;
cout << "5. Search element " << endl;
cout << "6. Exit " << endl;
}
int main() {
CircPtr cabezaLista = NULL, position;
int op;
string name;
double radius;
double x;
double y;
int pos;
do {
menu();
cin >> op;
switch(op)
{
case 1:
cout << "Write the name of the circle: ";
cin >> name;
cout << "\n Write radius: ";
cin >> radius;
do{
cout << "Invalid input. ";
cin >> radius;
}while(radius <= 0);
cout << "\n Write center: ";
cout << "X: ";
cin >> x;
cout << "Y: ";
cin >> y;
insertarCabeza(cabezaLista, name, radius, x, y);
break;
case 2:
cout << "Write the name of the circle: ";
cin >> name;
cout << "\n Write radius: ";
cin >> radius;
do{
cout << "Invalid input. ";
cin >> radius;
}while(radius <= 0);
cout << "\n Write center: ";
cout << "X: ";
cin >> x;
cout << "Y: ";
cin >> y;
insertarFinal(cabezaLista, name, radius, x, y);
break;
case 3:
cout << "Write the name of the circle: ";
cin >> name;
cout << "\n Write radius: ";
cin >> radius;
do{
cout << "Invalid input. ";
cin >> radius;
}while (radius <= 0);
cout << "\n Write center: ";
cout << "X: ";
cin >> x;
cout << "Y: ";
cin >> y;
cout << "Position : ";
cin >> pos;
posicion = buscarPosicion(cabezaLista, pos-1);
if (posicion != NULL)
insertarPosicion(posicion, name, radius, x, y);
break;
case 4:
cout << "\n\n Showing list : ";
escribirLista(cabezaLista);
break;
case 5:
cout << "\n Center of circle to search: ";
cout << "X: ";
cin >> x;
cout << "Y: ";
cin >> y;
buscarElemento(cabezaLista, x, y);
break;
case 6:
cout << "\n End of the program. ";
break;
}
cout << endl;
}while(op != 6);
return 0;
}

Answer 1

Just use while loop instead of do while loop. In your code because of cin you are taking one input value and for any value which user enters, next do while loop execute ones without checking condition so your prompting with invalid input on the correct radius input.
Instead of this
cout << "\n Write radius: ";
cin >> radius;
do{
cout << "Invalid input. ";
cin >> radius;
}while(radius <= 0);
Do like this
cout << "\n Write radius: ";
cin >> radius;
while(radius <= 0){
cout << "Invalid input. ";
cin >> radius;
}
Learn the basics of the loops.