【菜鸟求教】这个实在不太懂

E:\workspace\20120701\testc\main.c||In function 'main':|
E:\workspace\20120701\testc\main.c|6|warning: operation on 'a' may be undefined|
E:\workspace\20120701\testc\main.c|6|warning: operation on 'a' may be undefined|
||=== Build finished: 0 errors, 2 warnings ===|
这也算是未定义行为吗？