没有区别。signed与signed int与int是等价类型。在一些语法分析弱的编译器上，甚至与signed signed int与signed int signed与signed signed signed signed signed int都是等价类型。
一定要注意
char没有这种默认等价性。char不和signed char或者unsigned char其中任何一个等价。使用char的时候最好标明是signed char还是unsigned char。