#include<iostream>
#include<string.h>
#include<stdio.h>
using namespace std;
	string a;
int main()
{

	getline(cin,a);

	int len,sum=0;
	len = a.length();
	for (int i = 0; i < len; i++)
	{
		if (a[i] >= 48 && a[i] <= 57)sum++;
		if (a[i] >= 65 && a[i] <= 90)sum++;
		if (a[i] >= 97 && a[i] <= 122)sum++;
	}
	cout << sum;


	return 0;
}

为什么len = a.length()或者len=a.size()过得了，而len=strlen(a)过不了