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")

好像没加强多少

#include<bits/stdc++.h>
using namespace std;
int main()
{
	double a,b;
	char c;
	cin>>a>>b>>c;
	if(c=='+')
	{
		cout<<fixed<<setprecision(1)<<a+b;
	}
	else if(c=='-')
	{
		cout<<fixed<<setprecision(1)<<a-b;
	}
	else if(c=='*')
	{
		cout<<fixed<<setprecision(1)<<a*1.0*b;
	}
	else if(c=='/')
	{
		if(b==0)cout<<"除数不能为零";
		else cout<<fixed<<setprecision(1)<<a*1.0/b;
	}
	else cout<<"运算符有误";
	return 0;
} 

#include<bits/stdc++.h>
using namespace std;
int main(){
    double x,y;
    double a;
    char p;
    cin>>x>>y>>p;
    if(p=='+'){
        a=x+y;
        printf("%.1lf",a);
    }
    if(p=='-'){
        a=x-y;
        printf("%.1lf",a);
    }
    if(p=='*'){
        a=x*y;
        printf("%.1lf",a);
    }
    if(p=='/' and y!=0){
        a=x/y;
        printf("%.1lf",a);
    }
    if(p=='/' and y==0){
        cout<<"除数不能为零";
    }
    if(p!='+' and p!='-' and p!='*' and p!='/'){
        cout<<"运算符有误";
    }
    return 0;
}