C++ script: what is isdigit function doing in the script?

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C++

I wrote a script to understand the map STL better.
I wanted to verify user input was an integer, therefore I used isdigit to check the user input.

The input is an integer, and I am not certain isidigit is the best method to check if user input is an integer.

However, the if statement in which isdigit is being used only validates the variable if the condition is set to false and I do not understand why?

**NOTE: Kindly explain like I am 5.
Using simple objects for example like apples and oranges would be great.

I interpret this as: (expected results)
if(isdigit(x) == true)) {
then move to next step;
}

However, the actual results are:
if(isdigit(x) == false)) {
scripts runs;
}

int main()
{
	map<string, int>num_for_map, sec_num_for_map;

	char x;
	cout << "Enter an integer to map 'Num 1' to: " << flush;
	cin >> x;

	if (isdigit(x) == true) {
		char y;
		cout << "Enter a second integer to map 'Num 2' to: " << flush;
		cin >> y;

		if (isdigit(y) == true) {
			// Map key-value pairs using subscript[] and assignment operator
			num_for_map["Num 1"] = x;
			sec_num_for_map["Num 2"] = y;

			// Traverse through map
			for (auto a : num_for_map) {
				cout << a.first << " --> " << a.second << endl;
			}

			for (auto b : sec_num_for_map) {
				cout << b.first << " --> " << b.second << endl;
			}
		}

	}

	return 0;
}

What I have tried:

I tried setting if statement to true and this did not work.

I have tried using scanf but this also expects a false boolean value which Visual Studio does not like because it raises and error and states this function is not safe, to use scanf_s instead. I did so, with the same result.