#include main() {int y,a; y=2,a=1; while(y--!=-1) {do{a*=y;a

while(y-- != -1)//这句执行后y = 1
{
do{
a *= y;//a = 1;
a++;//a= 2
}while(y--);//这句执行后y = 0,do里面在执行一遍,即a = 1；推出do...while,来到外层while循环
后此时y = -1；外层循环不进入,但是y--还是要执行的故此时y = -2；a = 1
}