How to use switch with string?

[Furyoku]

I need to know of how to use switch with string.I know that we can use if and else instead. But I want to know of how to use string directly with switch.

[Peter87]

You can't. Use a chain of if, else-if.

if (str == "apple")
{
	std::cout << "grows on trees" << std::endl;
}
else if (str == "lion")
{
	std::cout << "a big cat" << std::endl;
}
else if (str == "turkey")
{
	std::cout << "a bird and a country" << std::endl;
}
else if (str == "guitar")
{
	std::cout << "an instrument" << std::endl;
}
else
{
	std::cout << "not sure what that is" << std::endl;
}

If you have many cases you can make the lookup more efficient (and possibly more convenient too) by using a map (std::map or std::unordered_map).

#include <iostream>
#include <map>

int main()
{
	std::map<std::string, std::string> m;
	m["apple"] = "grows on trees";
	m["lion"] = "a big cat";
	m["turkey"] = "a bird and a country";
	m["guitar"] = "an instrument";
	
	std::string str;
	std::cin >> str;
	
	std::map<std::string, std::string>::iterator it;
	it = m.find(str);
	if (it != m.end())
	{
		std::cout << it->second << std::endl;
	}
	else
	{
		std::cout << "not sure what that is" << std::endl;
	}
}

The above works fine when you only want to to lookup a value of a certain type but if you want different functionality in each case it's a bit more complicated. One way is to use a mix of switch and map, by having a map that lookup a value that you can use in the switch.

#include <iostream>
#include <map>

enum class Word // If you don't use C++11 or later you can use a normal enum
{
	apple,
	lion,
	turkey,
	guitar
};

int main()
{
	std::map<std::string, Word> m;
	m["apple"] = Word::apple;
	m["lion"] = Word::lion;
	m["turkey"] = Word::turkey;
	m["guitar"] = Word::guitar;
	
	std::string str;
	std::cin >> str;
	
	std::map<std::string, Word>::iterator it;
	it = m.find(str);
	if (it != m.end())
	{
		switch (it->second)
		{
		case Word::apple:
			// Do something
			break;
		case Word::lion:
			// Do something else
			break;
		case Word::turkey:
			// ...
			break;
		case Word::guitar:
			// ...
			break;
		}
	}
	else
	{
		std::cout << "not sure what that is" << std::endl;
	}
}

Another approach is to let the map map to a std::function of some kind and use lambda functions to set them conveniently. If you don't use C++11 you can get the same functionality by defining normal functions and having function pointers in the map.

#include <iostream>
#include <map>
#include <functional>

int main()
{
	std::map<std::string, std::function<void()>> m;
	m["apple"] = [](){ /* Do something */};
	m["lion"] = [](){ /* Do something else */};
	m["turkey"] = [](){ /* ... */};
	m["guitar"] = [](){ /* ... */};
	
	std::string str;
	std::cin >> str;
	
	std::map<std::string, std::function<void()>>::iterator it;
	it = m.find(str);
	if (it != m.end())
	{
		it->second();
	}
	else
	{
		std::cout << "not sure what that is" << std::endl;
	}
}