Question

Hallo

I have this assignment to print only alphabets in a C++ string. It works for most input but when [ and ] are present in the input they are printed as well.

#include <iostream>
#include <string>

using namespace std;

int main()
{
        string input = "THE QUICK BROWN FOX JUMPS OVER THE LAZY DOG]";

        for(int i=0;i<input.size();i++) 
        {
                if(input[i] >='A' && input[i] <= 'z')
                //if(isalpha(input[i]))
                        cout<<input[i];
        }
        cout<<endl;
        return 0;
}

Answer 1

The problem is here:

if(input[i] >='A' && input[i] <= 'z')
              ^^^                ^^^ 

You are using uppercase 'A' and lowercase 'z'.

The range A-z is not same as A-Z + a-z.
The ASCII value of Z is 90 and that of a is 97.

Between them there are 6 other characters which you are considering as alphabets.

ASCII value   Character
------------------------
90            Z 
91            [ \ 
92            \  \
93            ]   \  your range A-z includes these.
94            ^   /
95            _  /
96            ` /
97            a

To allow only uppercase and lowercase alphabets you should use:

if( (input[i] >='A' && input[i] <= 'Z') || (input[i] >='a' && input[i] <= 'z') )

or even better just use isalpa:

if(isalpha(input[i]))