Select single char from string using index?

Question

I'm trying to get the assembly code version of this action in C++. I made the following code.

#include <iostream>
#include <string>
#include <cstdlib>
#include <random>
using namespace std;

void RandomizeData();

string vowel = "AEIOU";
string consonant = "BCDFGHJKLMNPQRSTVWXYZ";
int Matrixes = 0;
int Rows = 0;
int Characters = 0;
int test;

int main()
{
    // declare variables

    while (Matrixes < 4)
    {
        while (Rows < 4)
        {
            while (Characters < 4)
            {
                RandomizeData();
                ++Characters;
            }
            Characters = 0;
            Rows++;
            cout << "\n";
        }
        Rows = 0;
        Characters = 0;
        cout << "\n\n";
        ++Matrixes;
    }

    cin >> test;

    return 0;
}

void RandomizeData()
{
    int randVowel = (rand() % 5);
    int randCons = (rand() % 21);

    test = (rand() % 2);

    if (test == 1)
    {
        cout << consonant[randCons] << "";
    }
    else
    {
        cout << vowel[randVowel] << "";
    }   
}

I have everything practically done for the asm. But, I still cannot get this section to work or translate it.

        ;How to do the following in asm?
        cout << consonant[randCons] << "";

The following is what I have so far: !!WARNING!! code is bad!

INCLUDE Irvine32.inc

.386
.stack 4096
ExitProcess proto,dwExitCode:dword


    .data

        vowels  DB  "AEIOU"
        cons    DB  "BCDFGHJKLMNPQRSTVWXYZ", 0
        path    DWORD   0
        cool    BYTE    ?                                   ;determines vowel or cons

        ;Loop counters
        rows    DWORD   0
        matrixes    DWORD   0
        characters  DWORD   0

        ;Random variables
        rndVowel        DWORD   ?
        rndCons     DWORD   ?



    .code
        main PROC 
            STEP1:  cmp     matrixes, 4
                    jge     STEP4

            STEP2:  cmp     rows, 4
                    jge     STEP1
                    mov     characters, 0

            STEP3:  cmp     characters, 4
                    jge     STEP2
                    call    CharSelector                ;get & display character
                    inc     characters              
                    jmp     STEP3                       ;repeat STEP 3

            STEP4:  invoke  ExitProcess,0
        main ENDP




        CharSelector PROC
            call    Randomize                           ;seed
            mov     eax, 2
            call    RandomRange
            mov     path, eax                           ;mov result to path

            STEP1:  cmp     path, 1
                    mov     ecx, 0
                    jne     STEP2   

            STEP2:                                      ;block chooses vowel index                                  
                    mov     eax, 5
                    call    RandomRange
                    mov     rndVowel, eax


                    ;How to do the following in asm


                    call    WriteString


                    exit

            STEP3:                                      ;block chooses cons index
                    mov     eax, 21
                    call    RandomRange
                    mov     rndCons, eax
                    exit
        CharSelector ENDP


    end main

Answer 1

The characters are one byte each, so just offset the base address of the array with your index.

It seems like you have your index in eax (the return value from RandomRange), so you should be able to do e.g.:

mov bl, [cons + eax]  ; read the character at index eax in cons, and place it in register bl