Translating a character array into a integer string in C++

Question

I was trying to achieve translating a character array into a integer string and corresponding character to their alphabetical order. For instance: A(a) = 0 , Z(z) = 25.

string key_char = argv[1];
string key_num;


    for (int i = 0; i < key_char.length(); i++){
        if (isalpha(key_char[i])){
            if (islower(key_char[i])){
                key_num[i] = int(key_char[i] - 97); //97 is the ascii value for 'a'
            }
            else{
                key_num[i] = int(key_char[i] - 65); // 65 is the ascii value for 'A'
            }

        cout << key_num << endl;

        }

My thought was to create two strings, key_char was to store command line input from the users in characters. key_num was to store the integer string after translation. I was thinking iterating through a loop and converting each character from the character array to the integer string through casting. I didn't receive any compiling errors, and it returned nothing either. Please let me know whether the idea of casting is viable in this situation or if there's a better solution to this matter. Thank you very much!

You need a separate index variable for writing to key_num e.g. key_num[j++], otherwise you will have empty spaces in key_num where isalpha(key_char[i]) is false — samgak
– samgak, Commented Jun 22, 2015 at 2:41
Hi there, I want a sequence of ints. For instance, if the users input "abz", I want my output string to be "0125" — Yu Zhou
– Yu Zhou, Commented Jun 22, 2015 at 2:41
Hi samgak, I am relatively new to programming, my understanding from your comment is that you can't share a index variable; in this case, these two strings. I don't quite understand why would isalpha would be false, do you mind explain a bit further! — Yu Zhou
– Yu Zhou, Commented Jun 22, 2015 at 2:47
isalpha would be false when the value isn't a letter , for example: '?' or '9' — Ryan Haining
– Ryan Haining, Commented Jun 22, 2015 at 2:50

Ryan Haining · Accepted Answer · 2015-06-22 02:53:31Z

3

If you want a sequence of int, then use a vector<int>. Using the key_char string, the values of the chars in it will serve as the initial value of the ints.

std::vector<int> key_num(key_char.begin(), key_char.end());

Then, iterate over each character of key_num and convert it to the equivalent int value

for (auto&& n : key_num) {
    n = std::toupper(n) - 'A';
}

or if you're in pre-c++11

for (std::vector<int>::iterator it = key_num.begin(), end = key_num.end();
        it != end;
        ++it) {
    *it = std::toupper(*it) - 'A';
}

After that you can print the ints

for (auto i : key_num) {
    std::cout << i;
}

You'll need to #include <cctype> and #include <vector> for this solution.

Your current approach is odd, the biggest problem is that the key_num you start with is an empty string, so you can't actually assign into it without fear of crashing.

edited Jun 22, 2015 at 2:53

answered Jun 22, 2015 at 2:45

Ryan Haining

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3 Comments

Yu Zhou Over a year ago

I am new to programming , and the concepts you have covered were a bit too advanced for me. I will definitely learn how vector works, thank you quite much!

Ryan Haining Over a year ago

A vector is a sequence that can grow. The four loop here is called a range-based for loop in c++, but is known more commonly as a for-each loop on other languages. The idea is just to say "for each element in some_sequence" rather than a loop that just counts

Yu Zhou Over a year ago

Thank you Ryan! That made a whole lot of sense!

UmNyobe · Accepted Answer · 2015-06-22 02:46:04Z

2

You can use directly literals 'a', 'A', because they are integers. Furthermore, key_char[i] - 'a' will evaluate to an integer, so no casting required.

If all you want is printing out you dont need an additional array.In the loop use

cout << (islower(key_char[i]) ? key_char[i] - 'a' : key_char[i] -'A')

and then

cout << std::endl

after the loop

answered Jun 22, 2015 at 2:46

UmNyobe

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Comments

timrau · Accepted Answer · 2015-06-22 02:49:21Z

2

You could use an std::ostringstream to construct the output string.

#include <sstream>
std::ostringstream strm;
for (int i = 0; i < key_char.length(); i++){
    if (isalpha(key_char[i])){
        if (islower(key_char[i])){
            strm << int(key_char[i] - 'a');
        }
        else{
            strm << int(key_char[i] - 'A');
        }
    }
}
key_num = strm.str();
std::cout << key_num << std::endl;

answered Jun 22, 2015 at 2:49

timrau

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