Stack around the variable was corrupted with pointer arithmetics

Question

With the code below, I'd always run into "Stack around the variable 'UserCode' was corrupted.

If I'm not mistaken, when I do userCode = (char*)malloc(sizeof(char)*N);, shouldn't it create an "array" with size of char*n ? I'm guessing my issue is either with my declaration of an array, or my pointer arithmetic.

Any help would be highly appreciated.

#include "stdafx.h"
#include <math.h>

int userPrompt1() {
    int numOfAlphabets = 0;
    printf("Please enter a number from 1 to 8 to choose how many alphabets you want\n");
        scanf_s(" %d", &numOfAlphabets);
        if (numOfAlphabets > 8 || numOfAlphabets < 0) {
            printf("Sorry! Invalid number entered. Try again. \n");
            numOfAlphabets = userPrompt1();
        }
        return numOfAlphabets;
}

int userPrompt2() {
    int numOfLetters = 0;
    printf("Please enter the number of letters you want to guess\n");
    scanf_s(" %d", &numOfLetters);
    if (numOfLetters < 0) {
        printf("Sorry! Invalid number entered. Try again. \n");
        numOfLetters = userPrompt2;
    }
    return numOfLetters;
}

int tryCalculator(int K, int N) {
    int tries = 0;
    tries = 1 + ceil(N * log2(K));
    return tries;
}

void codeGenerator(char codeGuessIn[], char letters[], int size) {
    for (int i = 0; i < size; i++) {
        int rando = rand() % size;
        codeGuessIn[i] = letters[rando];
        printf(" %c", codeGuessIn[i]);
    }
    printf("\n");
}

void codeChecker(char codeGuessIn[], char generatedCode[], int size) {
    int correctAlphabets = 0;
    for (int i = 0; i < size; i++) {
        if (codeGuessIn[i] == generatedCode[i]) {
            correctAlphabets++;
        }
    }
    printf(" %d in correct place \n", correctAlphabets);
}

void getUserCode(int size, char *userCode[]) {
    for (int i = 0; i < size; i++) {
        printf("Please enter letter #%d \n", i+1);
        getchar();
        scanf_s(" %c", &userCode[i]);
    }
}


int main(void)
{
    char letters[8] = { 'A','B','C','D','E','F','G','H' };
    char *generatedCode;    //array to hold generated code
    char *userCode;         // array to hold generated code.
    int K = userPrompt1();  //how many different alphabets in code
    int N = userPrompt2();  //how many letters in code
    int tries = tryCalculator(K, N);
    //int gameEnd = 1;

    userCode = (char*)malloc(sizeof(char)*N);
    generatedCode = (char*)malloc(sizeof(char)*N);
    codeGenerator(generatedCode, letters, N);
    getUserCode(N, &userCode);
    //codeChecker(userCode, generatedCode, N);


    return 0;
}

Answer 1

void getUserCode(int size, char *userCode[]) {
    scanf_s(" %c", &userCode[i]);

Here, userCode[i] is a char * (pointer-to-char), &userCode[i] is a char ** (pointer-to-pointer-to-char), and scanf("%c") expects a char *. A good compiler would warn about that.

I think what you meant to do here is something like:

void getUserCode(int size, char *userCode) {
    scanf_s(" %c", &userCode[i]);
}
int main(void) {
    char *userCode = malloc(N);
    getUserCode(N, userCode);
}

The printf(), getchar(), scanf() combination here reeks of the bad habits created by scanf: you're discarding the first character entered by the user because you're relying on an extra character in the input buffer. See http://c-faq.com/stdio/scanfprobs.html and read full lines of input with fgets() instead of using scanf().

Also,

int userPrompt2() {
    int numOfLetters = 0;
    ...
        numOfLetters = userPrompt2;
}

You're assigning a function pointer to an int. (A normal compiler should warn about this.) If the idea here is to call the function again to repeat the prompt in case the user enters something silly, it's probably a better idea to use a loop instead of a recursive call anyway.