Reading digits into an array and sorting it - arrays

Question

The task is as follows: to fill the file with numbers using the generation() function - an array cannot be used here. Then read the digits into the array by the read_file() function into the array and sort it using the quick sort method. Output to the console.
I wrote the code as I logically understood it myself, but a set of values is output to the console after sorting, as it is output in case of an error with a lack of memory, random numbers with cons sometimes. Maybe it's worth filling in a dynamic array? And why, if I know a specific number of elements?
Please help me figure it out.
#include <stdio.h>
#include <stdlib.h>
#define N 10
#define A -25000
#define B 25000
void generation();
void read_file();
void method_simple_sort();
int main(void) {
generation();
method_simple_sort();
return EXIT_SUCCESS;
}
void generation() {
FILE *file;
int i;
file = fopen("index.txt", "w");
srand(time(0));
for (int i = 0; i < N; i++) {
fprintf(file, "%d\n", A + rand() % (A - B + 1));
}
fclose(file);
}
void read_file() {
FILE *file;
int i, a[N] = { 0 };
file = fopen("index.txt", "r");
for (i = 0; i < N; i++) {
fscanf(file, "%d ", &a[i]);
}
fclose(file);
for (int i = 0; i < N; i++)
printf("%d ", a[i]);
}
void method_simple_sort() {
int a[N], i = 0, k = 0, ind_max = 0, temp = 0;
read_file();
for (k = 0; k < N - 1; k++) {
ind_max = k;
for (i = 1 + k; i < N; i++) {
if (a[i] > a[ind_max]) {
ind_max = i;
}
}
temp = a[k];
a[k] = a[ind_max];
a[ind_max] = temp;
}
// вывод результатов в файл
printf("\n\nПростого выбора: ");
for (int i = 0; i < N; i++) {
printf("%d ", a[i]);
}
printf("\n\n\n\n");
}

Answer 1

The function method_simple_sort defines a local array variable int a[N].
It then calls read_file(), but read_file() does not fill this local array variable defined in method_simple_sort.
Instead it fill its own local array variable (called also int a[N], but it's a different one than the one in method_simple_sort).
The bottom line is that when method_simple_sort attempts to sort a it sorts an array containing uninitialized data.
Hence the "garbaged" values that you see printed at the end.

Answer 2

The array used by the methods read_file and method_simple_sort aren't the same. When you declare anything inside a function it is translated at low level in space to allocate on the stack when you call the function.
You should transform read_file(void) into read_file(int *a) without declaring another instance of an array inside read_file.
By doing that you can pass a reference to the array declared inside method_simple_sort.
In particular:
void read_file(int *a) {
FILE *file;
int i;
/* a[N] = { 0 };*/
...
}
void method_simple_sort() {
int a[N], i = 0, k = 0, ind_max = 0, temp = 0;
read_file(a);
...
}