Why does the cin.fail() to work properly when I input a string or char?

[cowmil222]

EDIT.
Can someone please tell me why this crashes my IDE? so what I do is it prompts me to choose an option from a menu, and I input (for an example) wordssss. I made a while(cin.fail()) to catch it. here is my code.
(the code does simple math for you and will continue to run until the user inputs 5 to exit when prompted to enter input)

#include <iostream>
#include <string>

using namespace std;

double add(double , double );
double subt(double,double);
double multi(double,double);
double divi(double,double);


int main() {
    double x,z = 0;
    int r = 1;
    double xx, yy;
    
 do{
r = 1;
cout<<"Welcome to Glen's Handy Calculator"<<endl;
cout<<"     1. Addition "<<endl;
cout<<"     2. Subtraction "<<endl;
cout<<"     3. Multiplication "<<endl;
cout<<"     4. Division "<<endl;
cout<<"     5. Exit "<<endl;
cout<<"What would you like to do? ";

    
   cin >> x;
   
   while(r == 1){
   if (x ==1){
       cout<<"\nplease input two numbers seperated by spaces: ";
       
       cin>>xx>>yy;
       if(cin.fail()) {
        cout << "Error not an double please type something than hit enter: " << endl;
        cin.clear();
        cin.ignore(256,'\n');
        break;
       }
       else{
       cout<<endl;
       cout<<"this is the answer: "<<add(xx,yy)<<endl;
       r = 123;
       break;
       }
       
       
   }
   else if (x ==2){
       cout<<"\nplease input two numbers seperated by spaces: ";
       
       cin>>xx>>yy;
       cout<<endl;
        if(cin.fail()) {
        cout << "Error not an double please type something than hit enter: " << endl;
        cin.clear();
        cin.ignore(256,'\n');
        break;
       }
       else{
       cout<<"this is the answer: "<<subt(xx,yy)<<endl;
       r = 123;
       break;
       }
       
   }
   
      else if (x ==3){
       cout<<"\nplease input two numbers seperated by spaces: ";
       
       cin>>xx>>yy;
       cout<<endl;
       if(cin.fail()) {
        cout << "Error not an double please type something than hit enter: " << endl;
        cin.clear();
        cin.ignore(256,'\n');
        r = 3; 
        break;
       }
       else{
       cout<<"this is the answer: "<<multi(xx,yy)<<endl;
       r = 123;
       break;
       }
       
   }
   
         else if (x ==4){
       cout<<"\nplease input two numbers seperated by spaces: ";
       
       cin>>xx>>yy;
       cout<<endl;
       if(cin.fail()) {
        cout << "Error not an double please type something than hit enter: " << endl;
        cin.clear();
        cin.ignore(256,'\n');
        r = 123;
        break;
       }
       else{
       cout<<"this is the answer: "<<divi(xx,yy)<<endl;
       r = 123;
      break;
       }
      
       
   }
   
   else if(x == 5){
       cout<<"GOOD BYE";
       
       x = 69;
       r = 123;
       z = 12;
       break;
   }
   
else if(x>5 || x<=0){
cout<<"\nPlease try again"<<endl;
      r = 123;
       break;
}
   
   else{
    
        cout << "Error not an double please type something than hit enter: " << endl;
      r = 123;
        break;
    
   }
    
 }
 }while(z==0);



    
    
   
    

    return 0;
}

double add(double x, double y){
    double sum = x+y; 
    return sum;
}

double subt(double x, double y){
    double sub  = x-y;
    return sub;
}

double multi(double x, double y){
    double mul = x*y;
    return mul;
}
double divi(double x, double y){
    double divis = x/y;
    return divis;
}

TY,
I took of the while loop in the else statement because if all fails it has to go there, but it still crashes

[fiji885]

Examine line 105 carefully. Are you comparing?

[cowmil222]

ty meant to do == on 105

[cowmil222]

so when I am prompted with the menu if I type in any char or string it crashes. But if I chose a menu option and then input a string or a char, the error will prompt.

EDIT.
After I noticed on the test and run for this website, it just shows that, if i am prompted with the menu and i input a string or char, it will be an infinite loop of the menu and saying the error message which makes no sense why it should be doing that.

[fiji885]

Take a look at line 34. After you get a user input you want to check if that user input was compatible with whatever is being used to store said input.

std::cin >> x;
if(std::cin.fail())
{
    std::cin.clear();
    std::cin.ignore(256, '\n');
}