View Compilation Error

0_0_20043487_28375.c: In function 'main':
0_0_20043487_28375.c:5:39: error: 'chr4' undeclared (first use in this function)
  for(;scnaf("%c%c%c\n",&chr1, &chr3, &chr4) != EOF;)
                                       ^
0_0_20043487_28375.c:5:39: note: each undeclared identifier is reported only once for each function it appears in