Using The Result From An If Statement To Execute A Switch Cases?

I'm not sure if this will work. I'm assuming it should , I just can't figure out how.

I am trying to execute a Switch case from the result from an If Statement. For example if the result from the If is 1 , the first case executes

This is what I'm thinking:

#include <iostream>
using namespace std;

int main(){
    int opt;
    char input;

    cout<<"Enter something: ";
    cin> >input;

    if (input >=48 && input<=57){
        opt= 1;
    }

    switch(opt){
        case 1:
            cout<<"You have inputted a digit";
            break;

    }
    return 0;
}

Is what I'm thinking possible?