关于sscanf的提问

#include<iostream>
#include<string>
#include<cctype>
#include<vector>
#include<cstdio>
using namespace std;
int main()
{
	int i1,s2,s3;
	string str1,str2,str3,len,str0;
	char ch1;
	vector<string> ans;
	cin>>i1;
	for(int i=1;i<=i1;i++)
	{
		cin>>str1;
		if(isalpha(str1[0]))
		{
			ch1=str1[0];
			cin>>str2>>str3; 
		}
		else
	{
		str2=str1;
		cin>>str3;
	}
		sscanf(str2,"%d",&s2);
		sscanf(str3,"%d",&s3);
		if(ch1=='a')
			sprintf(str0,"%d+%d=%d",s2,s3,s2+s3);
		if(ch1=='b')
			sprintf(str0,"%d-%d=%d",s2,s3,s2-s3);
		if(ch1=='c')
			sprintf(str0,"%d*%d=%d",s2,s3,s2*s3);
		sprintf(len,"%d",strlen(str0));
		ans.push_back(str0);
		ans.push_back(len);
	}
	return 0;
}