为什么我不能在这里连接字符串

Question

#include <iostream>
#include <limits>
int main()
{
int i = 4;
d = 4.0;
string s = "HackerRank";
int a;
double b;
string c;                          

cin >> a; 
cin >> b;
cin >> c;

a = a + i;
b = b + d;

cout << a << endl;
cout << b << endl;
cout << "" + s + c;
return 0;
}
// Declare second integer, double, and String variables.
// Read and save an integer, double, and String to your variables.
// Note: If you have trouble reading the entire string, please go back and review the Tutorial closely.
// Print the sum of both integer variables on a new line.
// Print the sum of the double variables on a new line.
// Concatenate and print the String variables on ne
// The 's' variable above should be printed first.

Answer 1

您错过了添加包含字符串。此外，d变量的声明也不正确。你能用下面的代码试试吗。

#include <iostream>
#include <limits>
#include<string>

int main()
{
int i = 4;
double d = 4.0;
std::string s = "HackerRank";
int a;
double b;
std::string c;                          
std::cin >> a; 
std::cin >> b;
std::cin >> c;

a = a + i;
b = b + d;

std::cout << a << std::endl;
std::cout << b << std::endl;
std::cout << "" + s + c;
return 0;
}

Answer 2

包含的字符串标头操作员的过载<lt；对于std:：cout，仅在中定义，因此需要添加字符串标头。

#include <iostream>
#include <limits>
#include <string>
using namespace std;
int main(){
int i = 4;
float d = 4.0;
string s = "HackerRank";
int a;
double b;
string c;                          

cin >> a; 
cin >> b;
cin >> c;

a = a + i;
b = b + d;

cout << a << endl;
cout << b << endl;
cout << "" + s + c<<"n";
return 0;