babbage% gcc -o quarts-3 quarts-3.c && quarts-3
Enter volume in quarts: 4
4 quarts = 3.785334 liters
babbage% quarts-3
Enter volume in quarts: -5
Value of quarts must be nonnegative; enter value again: -2
Value of quarts must be nonnegative; enter value again: 1
1 quarts = 0.946333 liters