String toUpper & toLower [C++]

toUpperToLower.cpp

#include <iostream>
#include <vector>
#include <string>

using namespace std;

string toUpper(string str);
string toLower(string str);
vector<string> toUpper(vector<string> strings);
vector<string> toLower(vector<string> strings);

int main(int argc, char *argv[]) {
	
	string hello = "Hello World";
	hello = toUpper(hello);
	cout << hello << endl;
	
	cout << toUpper("hi girl") << endl;
	cout << toLower("HI how are YOU?") << endl;
	
	vector<string> names = {"daniel", "sofia", "noel"};
	names = toUpper(names);
	
	for (auto str: toUpper(names)) {
		cout << str << ' ';
	}
	
	return 0;
}

string toUpper(string str) {
	transform(str.begin(), str.end(), str.begin(), ::toupper);
	return str;
}

string toLower(string str) {
	transform(str.begin(), str.end(), str.begin(), ::tolower);
	return str;
}

vector<string> toUpper(vector<string> strings) {	
	for_each(strings.begin(), strings.end(), [](string& str){ str = toUpper(str); });
	return strings;
}

vector<string> toLower(vector<string> strings) {
	for_each(strings.begin(), strings.end(), [](string& str){ str = toLower(str); });
	return strings;
}