Question

I have a string “D”, that I want to convert into the integer 4.

(Additional information from OP)

D should convert into a decimal value . I want it to be “4”.

for D = “4” ; E = “5”; and so on…

It may have the combination . If AA comes ,the value should be 27 and ll increase consequetively.

Answer 1

It looks like this is what you want (based on your question and comments):

unsigned long long convert(string str)
{
    unsigned long long result = 0;
    for (int i = 0;i<str.length();i++)
        result+= (str[i] - 'A' + 1) + i*26;
    return result;
}

Now for "D" it will give 4, for "AA" it will give 1+26 = 27 and so on…