Reading digits into an array and sorting it


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) {
    return EXIT_SUCCESS;

void generation() {
    FILE *file;
    int i;
    file = fopen("index.txt", "w");
    for (int i = 0; i < N; i++) {
        fprintf(file, "%d\n", A + rand() % (A - B + 1));

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]);
    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;
    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]);

>Solution :

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.

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