If a cat is constipated, it will not be able to defecate, which may affect other things. It could be in pain and potentially stop eating, but the best thing to do is take it to a vet and get it treated.
Some symptoms of a constipated cats can include loss of appetite, vomiting, hardened abdomen, increased vocalization and straining to have a bowel movement, hard stool, bloating and abdominal discomfort when touched.
The first symptom is that it doesn't have bowel movements. That's also the second symptom, and the third. Cats usually defecate every day, if that doesn't happen, then it's constipation.
