C++ :

#include<bits/stdc++.h>
using namespace std;

int main(){
	double a,b;
	char c;
	cin>>a>>b>>c;
	if(c=='*'){
		printf("%.1lf",a*b);
	}
	else if(c=='/'&&b!=0){
		printf("%.1lf",a/b);
	}
	else if(c=='+'){
		printf("%.1lf",a+b);
	}
	else if(c=='-'){
		printf("%.1lf",a-b);
	}else if(c!='-'&&c!='+'&&c!='*'&&c!='/')cout<<"运算符有误";
	else if(c=='/'&&b==0) cout<<"除数不能为零";
}

Python :

# coding=utf-8
x=float(input())
y=float(input())
op=input()
if op=="+":
    z=x+y
    print(format(z,'.1f'))
elif op=="-":
    z=x-y
    print(format(z,'.1f'))
elif op=="*":
    z=x*y
    print(format(z,'.1f'))
elif op=="/":
    if y!=0:
        z=x/y
        print(format(z,'.1f'))
    else:
        print("除数不能为零")
else:
    print("运算符有误")