Count sequences of letters in a string - C++

Question

I'm working on a simple substitution-cipher decoder. I'm using frequency analysis to decrypt the ciphertext. Just looking at the frequency of unique letter isn't enough. I need to look at the occurrences of 2-letter sequences (maybe 3-letter sequences).

My code for counting the occurrences of each letter is below

int counterRaw[256][2] = {0};
    for(int i = 0; i <inputString.length(); i++)
        counterRaw[inputString[i]][1]++;

int counterLetter[26][2] = {0};
    for(int i = 0 ; i<26 ; i++){
        counterLetter[i][0] = 'A'+i;
        counterLetter[i][1] = counterRaw['A'+i][1];

As you can see very simple yet effective !

But I don't know how to achieve a 2-letter sequence counter, do you have any idea which could help me to code this ?

Thanks !

EDIT : As an example Given AZAZ RTYU JKLM I want my program to output :

AZ : 2
ZA : 1
ZR : 1
RT : 1
...

Answer 1

Something like the following would do the trick, though you'd have to do some jiggery pokery to make it suit your own needs.

#include <iostream>
#include <map>
#include <string>

int main ()
{
    std::string message("some string that you will probably get from some encrypted file");
    std::map<std::string,int> occurences;

    std::string seq("  ");
    for(int i = 1; i < message.length() - 1; i++)
    {
        seq[0] = message[i-1];
        seq[1] = message[i];

        //ignore spaces
        if (seq.compare(0,1, " ") && seq.compare(1,1, " "))
        {
            occurences[seq]++;
        }
    }

    //let's have a look ...
    for(auto iter = occurences.begin(); iter != occurences.end(); ++iter)
    {
        std::cout << iter->first << "   " << iter->second << "\n";
    }
    return 0;
}

output:

ab   1
at   1
ba   1
bl   1
cr   1
ed   1
en   1 
et   1
fi   1
fr   1
ge   1
ha   1
il   2
in   1
ll   1
ly   1
me   2
nc   1
ng   1
ob   1
om   3
ou   1
pr   1
pt   1
ri   1
ro   2
ry   1
so   2
st   1
te   1
th   1
tr   1
wi   1
yo   1
yp   1