I coded a program its for temperature conversion its still not developed yet and I'm having a problem.

Here's the code:

/* Software Name = Temperature Converter Calculator...
Made by Manzoor Ahmed.*/
// Program that helps converting Temperature degrees.
// Formulas obtained from wikipedia.org.

#include <cstdlib>
#include <cctype>
#include <iostream>

using namespace std;

int CelFunc() ;

void CnvrtTemp()
{
    char Cnvrt_Temp_Option ;


	     cout << "\n==================== Convert Temperature =======================" << endl ;
     do
      {
	     cout << "\n\n[C] Celsius Converter" << endl ;
	     cout << "[F] Fahrenheit Converter" << endl ;
	     cout << "[K] Kelvin Converter" << endl ;
	     cout << "[R] Rankine Converter" << endl ;
	     cout << "[M] Back to Main Menu." << endl ;
	


	     cout << "\n(Characters enclosed by the square brackets are the options.)" << endl ;
	
	     cout << "\nEnter your option: " ;
	     cin >> Cnvrt_Temp_Option ;

	     if ( Cnvrt_Temp_Option == 'C' || Cnvrt_Temp_Option == 'c' )
		    {
		     CelFunc();
		    }
		    
	     if ( Cnvrt_Temp_Option == 'F' || Cnvrt_Temp_Option == 'f' )
		    {
		     cout << "FahrFunc()" << endl ;
		    }
	
	     if ( Cnvrt_Temp_Option == 'K' || Cnvrt_Temp_Option == 'k' )
		    {
		     cout << "KelFunc()" << endl;
		    }

	     if ( Cnvrt_Temp_Option == 'R' || Cnvrt_Temp_Option == 'r' )
		    {
		     cout << "RankFunc()" << endl ;
		    }
	   } while (!( Cnvrt_Temp_Option == 'M' || Cnvrt_Temp_Option == 'm' ));
}

int main()
{
          char Main_Menu_Option;
                            // program name output
          cout << "################################################################################";
          cout << "#                                                                              #";
          cout << "#                                                                              #";
          cout << "#                                                                              #";
          cout << "#                       Temperature Converter Calculator                       #";
          cout << "#                                                                              #";
          cout << "#                                                                              #";
          cout << "#                                                                              #";
          cout << "#                                                                              #";
          cout << "################################################################################\n\n";


          do
            {                      // Main Menu

          cout << "\n================================ Main Menu =====================================\n\n\n";
                     // Menu
          cout << "[C] Convert Temperature" << endl ;
          cout << "[H] Help" << endl ;
          cout << "[E] Exit" << endl ;

          cout << "\n(Characters enclosed by the square brackets are the options.)\n" << endl ;



               cout << "\nEnter your option : ";
               cin >> Main_Menu_Option ;

             
               if (!( Main_Menu_Option == 'C' || Main_Menu_Option == 'c' || Main_Menu_Option == 'H' || Main_Menu_Option == 'h' || Main_Menu_Option == 'E' || Main_Menu_Option == 'e' ))
               {
                  cout << "\nWrong option entered\n";
               }



                if ( Main_Menu_Option == 67 || Main_Menu_Option == 99) // 67 == C , 99 == c.
                   {
                    CnvrtTemp();
                   }
				
				if ( Main_Menu_Option == 69 || Main_Menu_Option == 104 )
					{
						cout << "Help section is under construction.\n";
					}	


           } while (!( Main_Menu_Option == 69 || Main_Menu_Option == 101 ));
          system ("pause");
          return 0;
}

int CelFunc()
	{	char again;
		cout << "\n=============================== Celsius Converter ==============================\n\n" ;		
		
		
		do {
		cout << "Enter °C (Celsius) degree to convert :";
		double cTemp2Conv;
		cin >> cTemp2Conv;
		
			if (isdigit(cTemp2Conv)) {
				
				
				double cFahrenheit = (cTemp2Conv * 1.8) + 32;
				double cKelvin = cTemp2Conv + 273.15;
				double cRankine = (cTemp2Conv + 273.15) * 1.8;
				
				
				cout << "\nAnswer: " << cTemp2Conv << " Celsius in Fahnrenheit scale = " << cFahrenheit;
				cout << "\nAnswer: " << cTemp2Conv << " Celsius in Kelvin scale = " << cKelvin; 
				cout << "\nAnswer: " << cTemp2Conv << " Celsius in Rankine scale = " << cRankine;
				cout << "\n\n";
			}
			else {
				cout << "\nINVALID INPUT !";
				cout << "\nPlease enter numerical values.\n";
			}			
			cout << "\nDo you want to convert temperature again ?";
			cout << "\nEnter Y for yes, N for no.";
			cout << "\nEntering wrong option other than Y/N will result in getting back to \nConvert Temprature menu.";
			cout << "\n[y]/[n]:";
			cin >> again;
				
		} while (again == 'y'|| again == 'Y');
	}

Well the problem is when you go to Celsius Converter and their input a character then its starts looping infinitely. How to avoid looping ?
I used isdigit() here to check whether the input is a numerical value or its an alphabet.
I also used the cin.good() function but I'm still getting the same error.

Sorry if my code is too big but I couldn't lessen it because I'm a beginner and don't know where the real problem is.

I think the problem is that after cin >> Cnvrt_Temp_Option ; you need to strip the '\n' (Enter key) from the keyboard buffer. One way to do that is cin.ignore()

But I have problem in the CelFunc()

Anyway I'm gonna check it out

The Problem is in the CelFunc(), there when it asks for a number, but instead of inputting a number if you input an alphabet then it stars looping infinitely.

In CelFunc(), if you see the if statement its if (!(isdigit(cTemp2Conv))) not if (isdigit(cTemp2Conv))

You are using isdigit for double or int.but it wont return true.you may use for char.and if char is digit it will return true.so you may change your method for getting number from user.

Can any one tell me which method should I use ???

Just tell me the function I'm not saying that do it for me

string s;
cin>>s;
	
for(int i=0;i<s.length();i++)
	{
		if(isalpha(s[i]))
		{
			cout<<"error!!!!!!";
	        return -1;
	 				}

	}
	int a=atoi(s.c_str());

This is a basic test function.User cant input a alpha or alphanumeric string.

isdigit only works with a single character, not a double or int. doubles are always guarenteed to be all digits plus the decimal point so there's no point using isdigit with it. If you want to check that someone did not type a digit then use cin's error method if( cin.fail() )

Do i need to pass arguments in the cin.fail() function to check my input ?

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