I get WA on 14 test. Please give me tests!

Try with this:
2147000000 -2147000000
Output should be:
0

Check various test cases like
+ve -ve
+ve +ve
0 -ve
0 0
and check this tutorial http://www.techcrashcourse.com/2015/05/c-programming-arithmetic-operators.html

try zero

Yes