求解pow = inpow (n,p+1) / n;这个是如何成立的？

#include <stdio.h>
#include <stdlib.h> double inpow (double n, int p);
int main ()
{
int pow;
double num, sum; printf("Please enter a number and pow (q to quit ): ");
while (scanf ("%lf %d", &num, &pow) == 2 )
{
sum = inpow (num, pow);
printf("%g is %.4lf pow %d.\n", sum, num, pow);
printf("Please enter again (q to quit ): ");
} printf("Error!.\n");
system ("pause");
return 0;
} double inpow (double n, int p)
{
double pow = 1;
if (n != 0)
{
if (p < 0)
pow = inpow (n,p+1) / n;
else if ( p == 0 )
pow = 1;
else
pow *= inpow (n, p-1) * n;
return pow;
}
else
return 0;
}