Interactive, restrictive, dynamic user input - c

Question

I provided a link to a PDF of the assignment instructions.
[TL;DR]
Ask two questions: Are you afraid of the dark? Do you exercise?
Input: ‘Y’ for yes, ‘N’ for no.
If input to second question is 'Y', One additional question: Minutes per day exercised?
Input: Integer > 0. However, if less than 10 per day, unqualified.
Output: Tells the user whether they can to enter ninja training or not.
What I'm having difficulties with:
Dynamically Allocating a Multidimensional String Array
I have only been coding for about a week, and I understand it's probably overkill for this assignment. With that being said, I got an idea while doing this assignment, and while I find it rather challenging to articulate my idea with words, here's an image that I feel captures what I am "visualizing."
Visual posted on https://www.eskimo.com/~scs/cclass/int/sx9b.html by Steve Summit
In this particular assignment, I think it's a waste of memory to keep the user's answer's. Nevertheless, what if I want to write a program that ask the user for a series of inputs, and at the end, correlate them, or make spurious correlations for teh lulz?
Spurious Correlations http://www.tylervigen.com/spurious-correlations by Tyler Vigen
A more practical reason, however, an MBTI Personality Type test? I don't know exactly all the possibilities, but they seem exciting.
That's what I want to achieve with dynamically allocating a multidimensional string array
Will update later
Original post follows...
The code works but some inputs are still allowed, namely any characters entered if the the first element is either Y or N.
Here's the code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main() {
char reference[][2] = { "Y", "N" };
char (*ptr_reference)[2] = reference;
int reference_minutes[1] = { 10 };
int *ptr_reference_minutes = reference_minutes;
char **user_input;
user_input = (char**)malloc(3 * sizeof(char*));
int i;
for (i = 0; i < 3; i++) {
user_input[i] = (char*)malloc(4 * sizeof(char));
}
if (!user_input) {
printf("Could not allocate memory!/n");
exit(1);
}
i = 0;
while (i == 0) {
printf("\nAre you afraid of the dark? Choose either [Y/N], and press enter when finished: \n");
fgets(user_input[i], 4, stdin);
user_input[i] = realloc(user_input[i], sizeof(char));
if (strncmp(user_input[i], *ptr_reference, 1) == 0) {
printf("\nPatience, Young Grasshoper! You are not ready to become a ninja.");
i = 3;
break;
} else if (strncmp(user_input[i], *(ptr_reference + 1), 1) == 0) {
i++;
break;
} else {
printf("\nPlease enter Y for yes or N for no.\n\n");
continue;
}
}
while (i == 1) {
printf("\nDo you exercise? Input [Y/N], and press enter when finished: \n");
fgets(user_input[i], 4, stdin);
if (strncmp(user_input[i], *ptr_reference, 1) == 0) {
i++;
break;
} else if (strncmp(user_input[i], *(ptr_reference + 1), 1) == 0) {
printf("\nDo you even lift, Bro?");
i = 3;
break;
} else {
printf("\nPlease enter Y for yes or N for no.\n\n");
continue;
}
}
while (i == 2) {
int sscanf_result, answer;
printf("\nHow many minutes a day do you exercise? Type an integer greater than 9 and press enter when finished.\n");
fgets(user_input[i], 4, stdin);
sscanf_result = sscanf(user_input[i], "%d", &answer);
if ((sscanf_result == 0) | (sscanf_result == EOF)) {
/* either a non-integer entered or an end-of-line */
printf ("\nYou have to enter an integer!\n");
i = 2;
continue;
} else if (answer < *ptr_reference_minutes) {
printf("\nCome on! You kids are soft! You lack discipline!\n");
i = 3;
break;
} else {
printf("\nYou are a good fit for ninja training.\n");
for (i = 0; i < 3; i++) {
free(user_input[i]);
}
free(user_input);
user_input = NULL;
break;
}
}
return 0;
}

Answer 1

Ok, I could have a look at your program. The problem is not really in allocation but is indeed in string management. In C a string is a null terminated char array (please copy this 100 times...).
When you read a line with fgets, you get the new line character (\n) in your buffer, so if user types Y Enter you get {'Y', '\n', '\0', undeterminated_char }. The following realloc is then plain wrong:
it is likely to be a noop: the compiler shall only give you a buffer at least as large as your requirement. As 4 > 1, it can (and my implementation did) give the original buffer unchanged
you are not allowed to use anything past what you have required, and in particular, you shall not assume that there is a null!
So if you insist in doing a string comparison, you should only ensure that the second char is null: user_input[i][2] = '\0';
But IMHO what is required here is just:
if (user_input[i][0] == 'Y') {
...
That is not all. You try to do a great job in input processing, but just forgot one detail: if a line is longer than the declared size, fgets fills its buffer and leaves the remaining part of the line available for next read.
What follows is only my advice:
You have tried to use everything you know (and probably things you do not fully master...) into a single and simple program. Don't. Keep each program as simple as possible (Keep It Stupid Simple is a general good practice...), and trust your learner to give you other assignments for other patterns. So here you should:
read a line until you find the \n (it might require several fgets)
test the first character of the buffer to be 'Y' or 'N'
test the second one to '\0'
As it is a common requirement in real world, and only after your program works, you could considere:
ignoring initial blank characters
accept lower case as upper case
accept any character after first one (in order to accept Yes and No)
Last advice if nice coding matters for you: once your program works correctly, you should considere posting it in Code Review to get interesting comments on it.

Answer 2

#Serge Ballesta #Serga Ballesta Thank you kindly for your feedback. It was extremly helpful. After following your advice, I was able to write a better program, although, I'm not sure if I was successful in "Keep It Simple, Stupid."
I still can't figure out how to restrict characters after 'Y' or 'N', i.e., Nnb or Nq is accepted as N and goes through to the second question.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main (void) {
char *user_input = NULL;
user_input = (char*)malloc(3*sizeof(char));
int sscanf_result, answer;
int i;
while (!*user_input)
{
printf("\nAre you afraid of the dark? \n\nInput Specifications: Please type 'Y' to indicate yes, or 'N' to indicate no, and then press the 'Enter' or 'return' key when finished.\n\n");
i = 0;
fgets(user_input, sizeof(user_input), stdin);
/* trim off last character */
user_input[strlen(user_input)-1] = '\0';
if (user_input[i] == 'Y')
{
printf("\nFear of the dark? Fear those who lurk in the dark, my friend. Ninjas! You may not train as a ninja!");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
exit(0);
}
else if (user_input[i] == 'N')
{
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
printf("\nDo you exercise?\n\nInput Specifications: Please type 'Y' to indicate yes, or 'N' to indicate no, and then press the 'Enter' or 'return' key when finished.\n\n");
i = 0;
fgets(user_input, sizeof(user_input), stdin);
user_input[strlen(user_input)-1] = '\0';
if (user_input[i] == 'N')
{
printf("\nDo you even lift, Bro?\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
exit(0);
}
else if (user_input[i] == 'Y')
{
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
printf("\nHow many minutes a day do you exercise?\n\nInput Specifications: Please type a positive integer and press the 'Enter' or 'return' key when finished.\n\n");
i = 0;
fgets(user_input, sizeof(user_input), stdin);
user_input[strlen(user_input)-1] = '\0';
sscanf_result = sscanf(user_input, "%d", &answer);
if ((sscanf_result == 0) | (sscanf_result == EOF))
{
/* either a non-integer entered or an end-of-line */
printf ("\nPlease type a positive integer and then press the 'Enter' or 'return' key when finished.\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
continue;
}
if (answer < 10)
{
printf("\nCome on! You kids are soft! You lack discipline!\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
exit(0);
}
else
{
printf("\nYou may begin training as a ninja!\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
exit(0);
}
}
else
{
printf("\nInput Error: Please carefully read the input specifications that are provided after each question prompt and then try again.\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
continue;
}
}
else
{
printf("\nInput Error: Please carefully read the input specifications that are provided after each question prompt and then try again.\n");
free(user_input);
for (i = 0; i < 3; i++)
{
user_input[i] = '\0';
}
continue;
}
}
return 0;
}