大概就是这样

#include<iostream>
#include<string>
using namespace std;

int main(){
	string word;
	getline(cin,word);
	
	int ans=0;
	for(int i=0;i < word.size();i++){
		if(word[i] >= '0' && word[i] <= '9') ans++;
		else if(word[i] >= 'A' && word[i] <= 'Z') ans++;
		else if(word[i] >= 'a' && word[i] <= 'z') ans++;
	}
	
	cout << ans;
	
	return 0;
}