C++判断一个整形数的位数的几种写法

这里给出三种比较有代表性的写法：整除法（除10）；判断法（if）;数组法

//整除法
#include <iostream>
using namespace std;
int main()
{
	float num=0;
	float temp1=0;
	int flag=0;
	cout<<"please input a number from 0 to 9999:"<<endl;
	cin>>num;
	cout<<"the number you input is:"<<num<<endl;
	temp1=num;
	while(temp1>10)
	{
		temp1=temp1/10;
		flag++;
	}
	cout<<"the length of your number is:"<<flag+1<<endl;
}

//判断法（if法）
#include <iostream>
using namespace std;
int main()
{
	int num=0;
	int flag=0;
	cout<<"please input a number from 0 to 9999"<<endl;
	cin>>num;
	cout<<"the number that you have inputed is:"<<num<<endl;
	if(num>999&&num<=9999)
	{flag=4;}
	else if(num>99&&num<=999)
	{flag=3;}
	else if(num>9&&num<=99)
	{flag=2;}
	else
	{flag=1;}
	cout<<"the length of the number is:"<<flag<<endl;
	return 0;
}

//数组法
#include <iostream>
using namespace std;
int main()
{
	int flag=0;
	char num[5]={0};
	cout<<"please input a number from 0 to 9999:"<<endl;
	cin>>num;
	cout<<"the number that you have inputed is:"<<num<<endl;
	for(int i=0;i<5;i++)
	{
		if(num[i]!=0)
		{
			flag++;
		}
	}
	cout<<"the length of this number is:"<<flag<<endl;
}