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

char *expand(char *p)
{
    int len;
    char *q, ch;

    /* (1) */
    len = strlen(p);

    /* (2) */

    /* (3) */
    strcpy(q, p);

    /* (4) */

    /* (5) */
    free(p);

    /* (6) */
    return q;
}

int main(void)
{
    int i, n;
    char *str;

    str = malloc(sizeof(char)*2);
    str[0] = 'a';
    str[1] = '\0';

    printf("繰り返し回数を入力してください：");
    scanf("%d", &n);

    for ( i = 1; i <= n; i++ )
    {
        str = expand(str);
        printf("%3d:[%s]\n", i, str);
    }

    return 0;
}