其中的i--是什么意思 在第二个while前面？

Question

nt htio(char a[])
{
int i = 0;
int n = 1;
int sum = 0;

while (a[i] != '\0')
{
i++;
}
i--;
while (a[i] != 'X' && a[i] != 'x' &&i>=0)
{ 
if(a[i] >= '0' && a[i] <='9')
{
sum = sum + (a[i]-'0')*n;
i--;
n = n*16;
}
else if(a[i] >= 'a' && a[i] <= 'f')
{
sum = sum + (a[i] - 'a' + 10)*n;
i--;
n = n*16;
}
else if (a[i] >= 'A' && a[i] <= 'F')
{
sum = sum + (a[i] - 'A' + 10)*n;
i--;
n = n*16;
}
}
return sum;
}

Answer 1

while (a[i] != '\0'){i++;}这个循环结束后，i指向字符串a的结束标记的位置。将i-1后，i就指向字符串a的最后一个字符。