C语言求逆序数忽略负号

#include <stdio.h>
#include <math.h>

int main()
{
    int num=0,number,i,j,flag=0,k,sum=0;
    printf("input the number:");
    scanf("%d",&number);
    if(number<0)
        number*=-1;
    k=number;
    while(k!=0)
    {
        flag++;
        k/=10;
    }
    for(i=0;i<flag;i++)
    {
        num=number%10;

        for(j=0;j<flag-i-1;j++)
        {
            num=num*10;
        }
        sum+=num;
        number/=10;
    }
    printf("逆序数为：%d\n",sum);
    return 0;
}