归类了 OJ，整理了一下

XSM OJ 重庆小码王集团OJ/计算分数加减表达式的值.cpp

@@ -0,0 +1,20 @@
+#include <iostream>
+#include <iomanip>
+#include <cstring>
+#include <cstdio>
+#include <ctime>
+#include <cmath>
+using namespace std;
+int main(){
+	int a;
+	double sum1,sum2;
+	scanf("%d",&a);
+	for(int i=1;i<=a;i+=2){
+		sum1+=1*1.0/i;
+	}
+	for(int i=2;i<=a;i+=2){
+		sum2+=1*1.0/i;
+	}
+	printf("%.4lf",sum1-sum2);
+	return 0;
+}