array reverse output in c - c

Question

I do this program which receives input from a string and a substring, and then searches for the substring within the string by determining how often it appears (the number of occurrences) and the locations it is located, then these positions are inserted into an array for example (4 5 8) And they are printed correctly, now what I was trying to do, once I got my array with inside the locations where the substring was found it print it in reverse ie (8 5 4) I tried using this cycle
// reverse output
printf ("%d", count);
for (j = count - 1; j >= 0; j--)
    printf("%d", pos[j]);
But if the array positions are 8 5 4 so it prints to me
5 ,4, -311228772
Why does this happen? Here is the code:
// inclusion of libraries
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
 Reads a string allocated by the stream.
 It stops at newline, not included in string.
 Returns NULL to EOF
 */
char *my_getline(FILE *stream) { // statement of function
char *line = NULL; // this is just the pointer initialization
size_t pos = 0; // definition of position variables and init
int c; // a variable to store the temporary character
while ((c = getc(stream)) != EOF) // read every character until the end of the file
{
     char *newp = realloc(line, pos + 2); // To dynamically allocate memory, with reference to the number of characters and more '2' is only to compensate for the null character and the character (since it is 0)
     if (newp == NULL) { // checks whether memory has been properly associated or not.
         free(line); // if the line is not free the blank
         return NULL; // interrupts the program and returns NULL
     }
     line = newp; // if memory is allocated correctly stores the memory allocated to the line pointer
     if (c == '\n') // if a new line is detected
         break; // interrupts the while cycle
     line[pos++] = (char)c; // stores the character in dynamic memory and the new character in the new location.
}
if (line) { // if the line contains something then a null character is added at the end to complete that string.
    line[pos] = '\0';
}
return line; // returns the contents of the line.
}
int main(void) { // main statement
    char *str, *sub; // character punctuation statement
    size_t len1, len2, i, count = 0; // unsigned value statement "size_t is equal to unsigned int" so may also be <0
    int pos[count]; // declare a count array to insert the index then print it in reverse
int j;
// Here is the main string
    printf("Enter Main String: \n"); // print the entry and enter the main string
    str = my_getline(stdin); // inserts the entered string inside the pointer using my_getline function and using getchar analogue stdin to make the entered characters input from the standard input
    // here is the substring to look for
    printf("Enter substring to search: \ n"); // print the entry and enter the main substring
    sub = my_getline(stdin); // inserts the entered string inside the pointer using my_getline function and using getchar analogue stdin to make the entered characters input from the standard input
    if (str && sub) { // if string and substring && = and
        len1 = strlen(str); // inserts the string length in the len1 variable
        len2 = strlen(sub); // inserts the length of the string in the len2 variable
        for (i = 0; i + len2 <= len1; i++) { // loop for with the control that the substring is less than or equal to the main string ie len2 <= len1
            if (! memcmp(str + i, sub, len2)) { // here uses the memcmp function to compare the string and substring byte bytes
                count++; // count variable that is incremented each time the sub is found in p
                // here is where it gets in output
// If the substring was found mold the index with the locations it was found
pos[count] = i + 1;
printf( "%d\n", pos[count]);
            }
        }
// print to get reverse output
printf("number of times%d", count);
// print to get reverse output
printf("%d", count);
       for (j = count - 1; j >= 0; j--)
       printf("%d", pos[j]);
 
        if (count == 0) { // if count is = 0 ie the substring was not found string string not found
            // otherwise if not found
            printf("Subtry not found \n");
        }
    }
// free releases the memory area that was reserved for the string and substrings so that it can be reused in the next run
    free(str);
    free(sub);
    return 0; // exit analog
}

Answer 1

Your code is completely unreadable. Even reformatted and spaced out, the comments make it difficult to see the important stuff.
You should only comment the non obvious: int main(void) {// main statement is a good example of a useless counter productive comment.
After removing all comments, the code shows a few problems:
There is an extra space in printf("Enter substring to search: \ n");
The array pos is defined with a size of 0: int count = 0; int pos[count];. The program has undefined behavior.
count is incremented before storing the offset into the array. Hence the array contents does not start at index 0, hence producing incorrect output when you iterate from count-1 down to 0 in the second loop.
Here is a simplified and corrected version:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/*
Reads a string from the stream allocated with malloc
stops at newline, not included in string.
Returns NULL at EOF
*/
char *my_getline(FILE *stream) {
char *line = NULL;
size_t pos = 0;
int c;
while ((c = getc(stream)) != EOF) {
char *newp = realloc(line, pos + 2);
if (newp == NULL) {
free(line);
return NULL;
}
line = newp;
if (c == '\n')
break;
line[pos++] = (char)c;
}
if (line) {
line[pos] = '\0';
}
return line;
}
int main(void) {
printf("Enter Main String:\n");
char *str = my_getline(stdin);
printf("Enter substring to search:\n");
char *sub = my_getline(stdin);
if (str && sub) {
size_t count = 0;
size_t len1 = strlen(str);
size_t len2 = strlen(sub);
size_t pos[len1 + 1];
for (size_t i = 0; i + len2 <= len1; i++) {
if (!memcmp(str + i, sub, len2)) {
pos[count] = i + 1;
printf("%d\n", (int)pos[count]);
count++;
}
}
if (count != 0) {
printf("number of times: %d\n", (int)count);
for (size_t j = count; j-- > 0;) {
printf(" %d", (int)pos[j]);
}
printf("\n");
} else {
printf("substring not found.\n");
}
}
free(str);
free(sub);
return 0;
}

Answer 2

You declared pos as an array of length 0:
size_t ... count = 0;
int pos [count];
Thus, inside your for-loop you'll access some unitialized memory:
for (j = count-1; j>= 0; j--)
printf ("%d", pos [j]);