delete pics to save space

history_source/信息学奥赛一本通/2.4.1.cpp

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+#include<iostream>
+#include<string>
+#include<math.h>
+using namespace std;
+bool isop(string n)
+{
+	if(n=="+") return 1;
+	if(n=="-") return 1;
+	if(n=="*") return 1;
+	if(n=="/") return 1;
+	return 0;
+}
+double operation()
+{
+	string sr;
+	cin>>sr;
+	if(!isop(sr)) return atof(sr.c_str());
+	switch(sr[0])
+	{
+		case '+': return operation()+operation();
+		case '-': return operation()-operation();
+		case '*': return operation()*operation();
+		case '/': return operation()/operation();
+	}
+}
+int main()
+{
+	printf("%.6lf\n",operation());
+	return 0;
+}