C语言：求一个短整型正整数中的最大数字

unsigned int fun(unsigned int iValue)
{
unsigned int inputvalue = iValue;
unsigned int a = 0;
while(inputvalue)
{
unsigned int b = inputvalue % 10;
if(b >= a)
{
a = b;
}
inputvalue = inputvalue / 10;
}
return a;
}

#include<stdio.h>
#include<conio.h>
int main() {
int a=0;
int b[10];
int i=0, j=0;
int flag=0;

printf("please in put a number:");
scanf("%d",&a);

while (a%10>0) {
b[i++]=a%10;
a=a/10;
}

for (j=0; j<=i; j++) {
if (b[j]>flag)
flag=b[j];
}
printf("%d",flag);
}

int find_max_digit(int num)
{
int max_digit = 0;
while (num)
{
int tmp_digit = num % 10;
if (tmp_digit > max_digit)
{
max_digit = tmp_dig