C++ Console Even/Odd Control Without %,/,+ and -

[2kaud]

What does it return for an empty string? For VS2015 this code

#include <iostream>
#include <string>

using namespace std;

string EvenOdd_Finder(const string&);

int main() {
	string a = "h";
	cout << "a = \"h\" is an " << EvenOdd_Finder(a) << " value" << endl;

	a.clear();
	cout << "a.clear() is an " << EvenOdd_Finder(a) << " value" << endl;

	a = "";
	cout << "a = \"\" is an " << EvenOdd_Finder(a) << " value" << endl;
	return 0;
}

string EvenOdd_Finder(const string& input)
{
	const char lst = *input.crbegin();

	if (string("02468").find_first_of(lst) != string::npos)
		return "even";

	if (string("13579").find_first_of(lst) != string::npos)
		return "odd";

	return "bad";
}

displays

a = "h" is an bad value
a.clear() is an bad value
a = "" is an bad value

[Ramees219]

Same code i am using but error in 2013 visual studio

[2kaud]

The code works in release mode but gives this debug assertion message when compiled in debug mode as the original function assumed that input is not empty. Try

string EvenOdd_Finder(const string& input)
{
	if (input.size() == 0)
		return "bad";

	const char lst = *input.crbegin();

	if (string("02468").find_first_of(lst) != string::npos)
		return "even";

	if (string("13579").find_first_of(lst) != string::npos)
		return "odd";

	return "bad";
}

[Sikkirigi]

What you posted is just a function, not a complete program. In my post #6 I only provided replacement code for the function, not a complete program. A complete compilable program would be something like

#include <iostream>
#include <string>

using namespace std;

string EvenOdd_Finder(const string&);

int main()
{
	string a = "4521548568458745215a";

	cout << "this is an " << EvenOdd_Finder(a) << " value" << endl;
	return 0;
}

string EvenOdd_Finder(const string& input)
{
	const char lst = *input.crbegin();

	if (string("02468").find_first_of(lst) != string::npos)
		return "even";

	if (string("13579").find_first_of(lst) != string::npos)
		return "odd";

        return "bad";
}

If this doesn't compile then there is an issue with the compiler. However as RAD Studio XE8 is based upon the Clang c++11 compiler, the above should compile and run OK.

[bcc32 Error] File1.cpp(18): E2316 'crbegin' is not a member of 'string'
  Full parser context
    File1.cpp(17): parsing: string EvenOdd_Finder(const string &)

I get this error now.

[2kaud]

.crbegin() requires c++11. Try replacing

	const char lst = *input.crbegin();

with

	const char lst = *input.rbegin();

[Sikkirigi]

You saved the day again. Thanks mate.

[2kaud]

but this shows that the compiler you are using is not c++11 compliant. IMO you should consider upgrading to a version which is.

[GCDEF]

Thank u for correcting the code i hope u have to do that again

He shouldn't. Typically we provide guidance, rather than actually doing somebody's homework for them.

[2kaud]

He shouldn't. Typically we provide guidance, rather than actually doing somebody's homework for them.

Ramees219 post #5 didn't mention anything about homework.

and a Happy new Year

[GCDEF]

Ramees219 post #5 didn't mention anything about homework.

and a Happy new Year

Seems pretty obvious.

Happy new year to you too.

[Ramees219]

I respect that . Look i am not a good programmer like u guys because i don't get the chance to goto college or university i like learning programming now i am trying to learn from internet i aske questions when i am stuck . When i am stuck i need an example to know how it can done . So i just showed what i know from that i learned my mistake .
If someone take advantage of it in some time professor ask questions about the code right so he have to learn to answer it or he will regret later
All i am saying is i need help. Good night

[monarch_dodra]

Alternativelly, a lookup array (poor man's hash table) also works.

You can use a "const char*" to save on the space used by the array, at the cost of not using std::string:

#include <iostream>
#include <array>

using namespace std;

const auto Even_Odd_Array = [] {
    auto odd_even = array<const char*, 256>{};
    for (auto& p : odd_even)
        p = "bad";
    for (auto c : "02468")
        odd_even[c] = "even";
    for (auto c : "13579")
        odd_even[c] = "odd";
    return odd_even;
}();

const char* EvenOdd_Finder(const string&);

int main() {
	string a = "4521548568458745215";

	cout << "this is an " << EvenOdd_Finder(a) << " value" << endl;
	return 0;
}

const char* EvenOdd_Finder(const string& input) {
    return input.empty()
        ? "bad"
        : Even_Odd_Array[input.back()];
}

[monarch_dodra]

Also, note that all the solutions provided so far (mine included) are string based. Why not operate on actual numbers? You can easily test for parity with a bit tests (not forbidden according to requirements):

#include <iostream>

using namespace std;

int main()
{
	int number;
	std::cin >> number;
	cout << number << " is an " << (number & 1 ? "odd" : "even") << " value" << endl;
}

[tiliavirga]

Typically we provide guidance

Then I'd say there are two time-tested principles that apply in this case: Separation of Concern (SoC) and Keep it Simple Stupid (KISS).

SoC suggests we first check whether the input string is a valid integer syntactically, and only then whether it's odd or even.

KISS suggests we turn the rightmost digit into an integer using a standard C++ function and then apply a conventional odd/even test on that integer.

[2kaud]

Why not operate on actual numbers? You can easily test for parity with a bit tests (not forbidden according to requirements):

Ramees219 post #5 - which included some code to answer the question posed in post #1 - specifically mentions that Ramees219 is using strings for numbers. Hence the following posts relate to testing strings.

If an integer number is to tested for odd/even then monarch_dodra's code in post #28 can be used which is much more efficient than string testing.