Logic

If the ASCII value of a character lies between 65 (A) to 90 (Z) then it is an uppercase character or if the character’s ASCII value lies between 97 (a) to 122 (z) then it is a lowercase character.

See also: Find ASCII value of a character

See the flow diagram:

Program

LowerUpperCase.CPPCopy
#include <iostream>

using namespace std;

int main() {

    char ch;

    cout << "Enter any character : ";
    cin >> ch;

    if(ch >= 'A' && ch <= 'Z') {

        cout << endl << ch << " is UPPERCASE alphabet.";

    } else if(ch >= 'a' && ch <= 'z') {

        cout << endl << ch << " is LOWERCASE alphabet.";

    } else {

        cout << endl << ch << " is not an alphabet.";

    }

    return 0;
}
Try It

Output

Enter any character : S
S is UPPERCASE alphabet.