Exception/throw handling, how can I throw an integer value when the calculation is over or under a certain amount?

Here is what I have in my program so far, if Celsius is under 100 it should throw integer value of 1, if the Celsius is above 100, it should throw the integer 2.

#include<iostream>
using namespace std;

int a = 1;
int b = 2;

int tempconversion() {
   int f, c;
   cout << "Enter temperature in Fahrenheit: ";
   cin >> f;
   c = (f-32)/1.8;
   cout<<"Tempature in celsius is: "<<c;
   return c;

 try {
        if( c < 0 ) {
            throw a;
   }
}
   catch (int a) {
       cout<<"Celsius below zero"<<endl;
    }

   try{
        if( c > 100 ) {
      throw b;
   }
}
    catch (int b){
        cout<<"celsius above 100"<<endl;
    }

}
int main(){
   tempconversion(); 
}