[C]reads an integer and return the reversing digits.

這邊提供兩總方法作為解決方案，第一種比較直觀直接印出餘數，第二種則採取真實將數值逆轉。
以下程式碼供大家參考
方法1

#include <stdio.h>
#include <stdlib.h>

int reversing(long int);

int reversing(long int number)
{
	while(number > 0)
	{
		printf("%d",number%10);
		number=number/10;
	}
	return 0;
}
void main (void)
{
	long int number;
	printf("please enter number > ");
	scanf("%d",&number);
	printf("The reversing of %d is ",number);
	reversing(number);
	printf("\n");
	system("pause");
}

方法2

#include <stdio.h>
#include <stdlib.h>

int reversing(long int);

int reversing(long int number)
{
	long int result=0,temp,ten_pow=1;
	int k=0;
	temp=number; //計算次數前先把數字存起來
	//--------計算最大是十的幾次方--------
	while(number > 0)
	{
		number=number/10;
		k++;
	}
	//--------計算剛剛的十的N次方是多少
	number=temp;
	for(int i=1;i<k;i++)
		ten_pow=ten_pow*10;
	//-------逐一取餘數，並乘上十的N次方或N-1次方等等
	while(number > 0)
	{
		result=result+((number%10)*ten_pow);
		number=number/10;
		ten_pow=ten_pow/10;
	}
	//傳回結果
	return result;
}
void main (void)
{
	long int number;
	printf("please enter number > ");
	scanf("%ld",&number);
	printf("The reversing of %ld is %d",number,reversing(number));
	printf("\n");
	system("pause");
}