Look for a data structure like sets in Pascal

[Nikko YL]

In Pascal, I can write a boolean expression like ch in ['Y', 'y', 'N', 'n'] to find whether the character ch is one of the characters in the Pascal set

I looked up set and unordered_set in the reference page but can't find a method to do this.

I don't want to write the tedious code like the following.

  (ch == 'Y') || (ch == 'y') || (ch == 'N') || (ch == 'n')

Is there a handy way to accomplish the same thing in C++?

[MiiNiPaa]

#include <iostream>

bool contain(const std::string& s, char c)
{
    return s.find(c) != std::string::npos;
}

int main()
{
    char c;
    std::cin >> c;
    std::cout << contain("YyNn", c);
}

Or if you want generality and use something aside from chars in the future:

#include <unordered_set>
#include <iostream>
#include <vector>
#include <algorithm>

template <typename T>
bool contain(const std::unordered_set<T>& C, T val)
{
    return C.find(val) != C.cend();
}

template <class T, typename V>
bool contain(const T& C, V val)
{
    return std::find(C.cbegin(), C.cend(), val) != C.cend();
}

int main()
{
    std::unordered_set<char> booleans {'Y', 'y', 'N', 'n'};
    std::vector<int> ints{1, 3, 4, 7};
    char c;
    std::cin >> c;
    int i;
    std::cin >> i;
    std::cout << contain(booleans, c) << '\n' <<
                 contain(ints, i);
}

[Nikko YL]

What about dealing with integer?

int x;
std::cin >> x;
if ( (x == 1) || (x == 3) || (x == 7) )
   std::cout << "You win\n";

How can I rewrite line 3?

[MiiNiPaa]

I have updated my post. You can use those templated helper functions to find if value is contained inside any STL container

[JLBorges]

#include <iostream>
#include <initializer_list> // http://en.cppreference.com/w/cpp/utility/initializer_list

template < typename T, typename U >
bool in( const T& value, const std::initializer_list<U>& set )
{
    for( auto& v : set ) if( v == value ) return true ;
    return false ;
}

int main()
{
    char ch ;
    std::cin >> ch ;

    if( in( ch, { 'Y', 'y', 'N', 'n' } ) ) std::cout << "ok\n" ;
    
    int i = 7 ;
    if( in( i, { 1, 3, 5, 7, 9 } ) ) std::cout << "ok\n" ;
    
}

http://coliru.stacked-crooked.com/a/f51a430930def92c

[Nikko YL]

This seems even more complicated than simply typing all possibility.
So is there no easy approach which I can do this by a few code?

[nvrmnd]

the one with the fewest code and simplest way is actually your original approach

http://www.cplusplus.com/reference/initializer_list/initializer_list/?kw=initializer_list

http://www.cplusplus.com/doc/oldtutorial/templates/

http://www.cplusplus.com/doc/tutorial/control/ (see the ranged based for loop section)

[MiiNiPaa]

You need to write these helper function once. Put them into header file and Just include it in any new project. Your code will look like:

#include <iostream>
//...
#include "includes.h"

int main()
{
    char c;
    std::cin >> c;
    if ( !in(c, {'Y', 'y', 'N', 'n'}) ) {
        std::cout << "invalid input\n";
}