这个程序的执行过程是怎样的，结果为什么是8.000000？
#include<stdio.h>void sub(double x, double *y, double *z)
{
*y = *y - 1.0; *z = *z + x;
}
main()
{
double a = 2.5, b = 9.0, *pa, *pb;
pa = &a; pb = &b;
sub(b - a, pa, pa);
printf("%f\n", a);
}
相当于：
double x;
x = b - a;
a = a - 1.0;
a = a + x;
printf("%f\n", a);