You need a semicolon after the declaration of class human (unless you want to right away specify what variables would be of this type).
It's not an error, but classes usually are spelt according to upper CamelCase (or PascalCase).
When you try to print out the age, height and location they are private and can be accessed only within the class. You could make them public, but in that case, there's no point having the setter methods. Instead, you could create getter methods (alongside the setter methods).
Not an error, but again very strange to have a setter method return any value.
One more thing: you declare your class within the main() function. So the type class Human is only visible within the main function and not outside of it. If you are not happy with this, you should move the class declaration outside of your main() function.
You should use the #include statements to have references to standard input/output manipulations as well as have access to strings.
At the end of your main() function, you should return a value, since it is not a void function. Typically 0 indicates everything was fine.
I'd fix your code as below:
#include <iostream>
#include <string>
int main()
{
class Human
{
private:
int age;
int height;
std::string location;
public:
void set_age(int new_age) { age = new_age; }
int get_age() const { return age; }
void set_height(int new_height) { height = new_height; }
int get_height() const { return height; }
void set_location(std::string new_location) { location = new_location; }
std::string get_location() const { return location; }
};
Human hello;
hello.set_age(25);
hello.set_height(15);
hello.set_location("PK");
std::cout << hello.get_age() << " " << hello.get_height() << " " << hello.get_location() << std::endl;
return 0;
}