everest% cc scan6.c
everest% 

everest% a.out
Enter an integer: 1
r = 1 d = 1
Enter another integer: 2
r = 1 d = 2
everest% 

everest% a.out
Enter an integer: a
Try again, enter an integer: abc
Try again, enter an integer: 6
r = 1 d = 6
Enter another integer: 21
r = 1 d = 21
everest% 

everest% a.out
Enter an integer: xyz
Try again, enter an integer: abc
Try again, enter an integer: 17 abc
r = 1 d = 17
Enter another integer: 2
r = 1 d = 2
everest%