#include <cctype>

int main()
{

char c1, c2;
  int invalue;

  // stuff here to get the chars

  if (!std::isdigit(c1) || !std::isdigit(c2)) {
   // do whatever you must for invalid inputs
  }
  else {
    invalue = (c1 - '0') * 10 + (c2 - '0');

    switch(invalue) {
      case 0: cmd0();
              break;

      case 3: cmd3();
              break;

       // other valid cases here

      default: // error routine here for invalid input numbers

    }
  }
}