Avodi if else statement

I have a some problem that is confuse me. I have a lot of if else statemenent in my code, and I want to avoid those if-else statement and do in a way that is easiest. I tried switch, but doesn't work because I should get the month in the output and have no idea. Any suggesten ??

if('j' == c1)
    if('a' == c2)
      mnth = 1;
    else
      if ('u' == c2)
        if('n' == c3)
           mnth = 6;
         else if ('l' == c3)
           mnth = 7;
        else error(c1, c2, c3);
      else error(c1, c2, c3);
  else
     if('f' == c1)
       if('e' == c2)
          if('b' == c3)
             mnth = 2;
          else error(c1, c2, c3);
       else error(c1, c2, c3);
   else
     if('m' == c1)
        if('a' == c2)
           if('y' == c3)
              mnth = 5;
           else
             if('r' == c3)
               mnth = 3;
              else error(c1, c2, c3);
        else error(c1,c2,c3);
     else
        if('a' == c1)
          if('p' == c2)
             if('r' == c3)
                mnth = 4;
             else error(c1, c2, c3 );
          else
             if('u' == c2)
                if('g' == c3)
                   mnth = 8;
                else error(c1,c2,c3);
             else error(c1,c2,c3);
        else
          if('s' == c1)
             if('e' == c2)
                if('p' == c3)
                   mnth = 9;
                else error(c1, c2, c3);
             else error(c1, c2, c3);
          else
             if('o' == c1)
                if('c' == c2)
                   if('t' == c3)
                      mnth = 10;
                   else error(c1, c2, c3);
                else error(c1, c2, c3);
             else
                if('n' == c1)
                   if('o' == c2)
                      if('v' == c3)
                         mnth = 11;
                      else error(c1, c2, c3);
                   else error(c1, c2, c3);
                else
                   if('d' == c1)
                      if('e' == c2)
                        if('c' == c3)
                            mnth = 12;
                        else error(c1, c2, c3);
                       else error(c1, c2, c3);
                   else error(c1, c2, c3);