[kolleykibber]

Well that post just cost me a couple of hours.

And still 136 bytes off 431:

  #define p printf 
  int main(){const char *g[]={"A Partridge in a Pear 
  Tree.\n","Two Turtle Doves, and","Three French Hens,","Four 
  Calling Birds,","Five Gold Rings,"," Geese-a-Lay"," Swans- 
  a-Swimm","t Maids-a-Milk","e Ladies Danc"," Lords-a-Leap"," 
  Pipers Pip","Twelve Drummers Drumm"};
  const char *d[{"First","Second","Third","Four","Fif","Six","Seven","Eigh","Nin","Ten","Eleven","Twelf"};for(int i=0,j;i<12;i++){p("On 
  the %s%s day of Christmas\nMy true love sent to 
  me\n",d[i],i>2?("th"):"");
  for(j=i;j>=0;j--){p("%s%s%s\n",j>4&&j<11? 
  d[j]:"",g[j],j>4?"ing,":"");}}}

[huhtenberg]

You can shave 25 more by using printf as is, removing "const", removing spaces between char and *, and removing parenthesis around "th".

[tgv]

Are those consts really necessary? There are also a few character missing after char *d.

[mananaysiempre]

> Are those consts really necessary?

Technically yes, initializing a plain char * from a const char * (from array decay) is a constraint violation (an error the standard requires the compiler to detect and complain about) even in C89. Many compilers will let you off with a warning though.

[junon]

which characters are missing?

[huhtenberg]

"]=" after "*d["

[junon]

It's not necessary in C.

[huhtenberg]

   const char *d[{"First","Second",...,"Twelf"};

is not a valid C unconditionally.

[tgv]

You should tell my compiler.