Exception Thrown when attempting to compare using pointers - c

Question

I am trying to make a loop that makes a pointer point to different elements in an array (Sorting in descending order) and I can't seem to get the comparing correctly since I always get an exception thrown. I also have a loop to print all the pointer's elements to test if the loop worked correctly. Never really used pointers before, but I tried to format them the same way I've seen on other websites when studying pointers. This is the part of code I am talking about:
//What I have included
#define _CRT_SECURE_NO_WARNINGS
#define MAX 5
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
//Variables related to the loops
int nums[MAX], *ptrd[MAX];
//Loops in question (Assume nums[MAX] = {1, 2, 3, 4, 5})
for (int i = 0; i < MAX; i++)
{
for (int j = 0; j < MAX; j++)
{
if (*ptrd[i] < nums[j] && nums[j] <= *ptrd[i - 1])
{
if (i > 0)
{
if (ptrd[i] == ptrd[i - 1])
continue;
}
ptrd[i] = &nums[i];
}
}
}
for (int i = 0; i < MAX; i++)
{
printf("\n%d", *ptrd[i]);
}
Current full code so far (note the code in question here is different):
#define _CRT_SECURE_NO_WARNINGS
#define MAX 5
#include <stdio.h>
#include <ctype.h>
#include <stdbool.h>
#include <stdlib.h>
//Variables
char input[20];
int nums[MAX], *ptrd[MAX], *ptra[MAX];
bool isValid;
//Methods
bool checkValidity();
void convertChars();
void resetInput();
int main()
{
printf("Please enter 5 numbers (Separate each by spaces): ");
input:
resetInput();
scanf(" %[^\n]%*c", &input);
isValid = checkValidity();
if (isValid == false)
{
printf("Invalid input. Retry: ");
goto input;
}
convertChars();
for (int i = 0; i < MAX; i++)
{
for (int j = 0; j < MAX; j++)
{
if (*ptrd[i] < nums[j])
{
if (i > 0)
{
if (ptrd[i] == ptrd[i - 1])
continue;
if (nums[j] <= *ptrd[i - 1])
ptrd[i] = &nums[i];
}
else
ptrd[i] = &nums[i];
}
}
}
for (int i = 0; i < MAX; i++)
{
printf("\n%d", (*ptrd)[i]);
}
getchar();
return 0;
}
bool checkValidity()
{
bool multNum = false;
int chars = 0;
for (int i = 0; i < 20; i++)
{
if (!isdigit(input[i]))
{
if (input[i] == ' ' && multNum == true || input[i] == NULL && multNum == true)
chars += 1;
if (input[i] != ' ' && input[i] != NULL)
{
printf("\nIncorrect characters\n");
return false;
}
if (input[i] == ' ' && multNum == false)
{
printf("\nToo many spaces at at once\n");
return false;
}
if (input[i] == ' ' && multNum == true || input[i] == NULL && multNum == true)
multNum = false;
}
else if (isdigit(input[i]))
{
multNum = true;
}
}
if (chars != 5)
{
printf("\nIncorrect amount of nums (%d)\n", chars);
return false;
}
else
return true;
}
void convertChars()
{
int placeHolder, nums_ = 0, done = 0;
for (int i = 0; i < 20 && done < 5; i++)
{
if (isdigit(input[i]))
{
placeHolder = input[i] - '0';
nums_ = (nums_ * 10) + placeHolder;
}
else
{
nums[done] = nums_;
nums_ = 0;
done += 1;
}
}
}
void resetInput()
{
for (int i = 0; i < 20; i++)
{
input[i] = NULL;
}
}

Answer 1

You didn't initialize *ptrd[MAX], which results in an undefined behavior. Run your code with gdb, and it crashes with following output:
(gdb) run
Starting program: /home/pringles/Desktop/a.out
Please enter 5 numbers (Separate each by spaces): 3 2 1 5 6
Program received signal SIGSEGV, Segmentation fault.
0x0000000000400719 in main () at test.c:37
37 if (*ptrd[i] < nums[j])
By printing the elements in ptrd, you can see all the elements point to 0x0:
(gdb) print ptrd
$1 = {0x0, 0x0, 0x0, 0x0, 0x0}