/* Now OK - but tedious */

#include <stdio.h>
#include <stdlib.h>

enum grade_simple {not_passed, passed};

enum grade_7 {g7_minus_tre = -3, g7_nul_nul = 0, g7_nul_to = 2, g7_fire = 4,
              g7_syv = 7, g7_ti = 10, g7_tolv = 12};

enum grade_13 {g13_nul_nul = 0, g13_nul_tre = 3, g13_fem = 5,   
               g13_seks, g13_syv, g13_otte, g13_ni, g13_ti, g13_elleve, 
               g13_tretten = 13};                         

enum grade_7 convert_grade_13_to_grade_7 (enum grade_13 g13){
  enum grade_7 g7; 

  switch(g13){
    case g13_nul_nul:   g7 = g7_minus_tre; break;
    case g13_nul_tre:   g7 = g7_nul_nul; break;
    case g13_fem:       g7 = g7_nul_nul; break;
    case g13_seks:      g7 = g7_nul_to; break;
    case g13_syv:       g7 = g7_fire; break;
    case g13_otte:      g7 = g7_syv; break;
    case g13_ni:        g7 = g7_syv; break;
    case g13_ti:        g7 = g7_ti; break;
    case g13_elleve:    g7 = g7_tolv; break;
    case g13_tretten:   g7 = g7_tolv; break;
    default:
      printf("Illegal grade in grade_13 encountered. Bye.");
      exit(EXIT_FAILURE);
  }

  return g7;
}

void prnt_grade_7(enum grade_7 g){
  switch (g) {
    case g7_minus_tre: printf("minus-tre"); break;
    case g7_nul_nul: printf("nul-nul"); break;
    case g7_nul_to: printf("nul-to"); break;
    case g7_fire: printf("fire"); break;
    case g7_syv: printf("syv"); break;
    case g7_ti: printf("ti"); break;
    case g7_tolv: printf("tolv"); break;
    default:
        printf("Illegal grade in grade_7 encountered. Bye.");
        exit(EXIT_FAILURE);
  }
}  
    
int main(void){
  
  int grade_number; 
 
  printf("Enter '13 skala' grade: ");
  scanf(" %d", &grade_number);

  printf("7-step grade is: ");
  prnt_grade_7(
         convert_grade_13_to_grade_7((enum grade_13)grade_number));    /* Notice the type cast */
  printf("\n");

  return 0;
}