double_last_name

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

typedef struct student
{
    char *last_name;
    char *name;
    int height;
}student_t;

student_t *journal_create(student_t* journal, int max_size)
{
    journal = malloc(sizeof(student_t) * max_size);
    if (!journal)
        return NULL;

    return journal;
}

void j_delete(student_t* journal, int size)
{
    for (int i = 0; i < size; i++)
    {
        free((journal + i) -> name);
        free((journal + i) -> last_name);
    }
    free(journal);

    return;
}

student_t *journal_input(student_t* journal, int *size, int max_size)
{
    char tmp[256];

    if ((scanf("%s", tmp) != 1))
    {
        j_delete(journal, *size);
        return NULL;
    }

    (journal + *size) -> last_name = malloc(strlen(tmp) + 1);
    strcpy((journal + *size) -> last_name, tmp);


    if ((scanf("%s", tmp) != 1))
    {
        j_delete(journal, *size);
        return NULL;
    }

    (journal + *size) -> name = malloc(strlen(tmp) + 1);
    strcpy((journal + *size) -> name, tmp);

    int height;
    if ((scanf("%i", &height) != 1))
    {
        j_delete(journal, *size);
        return NULL;
    }

    (journal + *size) -> height = height;
    (*size)++;

    return journal;
}

void journal_output(student_t *journal, int size)
{
    for(int i = 0; i < size; i++)
    {
        printf("data about student №%d is ", i);
        printf("%s %s %d", (journal + i) -> last_name, (journal + i) -> name, (journal + i) -> height);
        printf("\n");
    }
}

void journal_double(student_t *journal, int size)
{
    char *tmp = NULL;

    for(int i = 0; i < size; i++)
    {
        tmp = malloc(strlen((journal + i) -> last_name) * 2 + 1);
        snprintf(tmp, strlen((journal + i) -> last_name) * 2 + 1, "%s%s", (journal + i) -> last_name, (journal + i) -> last_name);
        char* ln_tmp = NULL;
        ln_tmp = realloc((journal + i) -> last_name, (strlen(tmp) + 1) * sizeof(char));
        if(!ln_tmp)
            j_delete(journal, size);

        (journal + i) -> last_name = ln_tmp;
        strcpy((journal + i) -> last_name, tmp);
        free(tmp);
    }
}