코딩 과제 중 질문입니다

 
printf("input file name? ");
scanf("%s", input_str);
 
input_file = fopen(input_str, "r");
if (input_file == NULL)
{
	fprintf(stderr, "File %s not found\n", input_str);
	return 0;
}

#include <stdio.h>
#include <malloc.h>
#define INFY 987654321;
 
FILE *input_file, *output_file;
int **M, **P;
 
int** array_malloc(int n)
{
	int** array;
	int i, j;
 
	/* array allocate */
	array = (int**) malloc(0);
	for (i = 0; i <= n; i++)
		array[i] = (int*) malloc(sizeof(int) * n);
 
	/* init array */
	for (i = 1; i <= n; i++)
		for (j = 1; j <= n; j++)
			array[i][j] = 0;
 
	return array;
}
 
void print_order(int i, int j)
{
	int n;
 
	if (i == j)
		fprintf(output_file, "A%d ", i);
	else
	{
		n = P[i][j];
		fprintf(output_file, "( ");
		print_order(i, n);
		print_order(n + 1, j);
		fprintf(output_file, " )");
	}
}
 
void minmult(int n, int* d)
{
	int i, j, k, q;
 
	M = array_malloc(n);
	for (i = 1; i <= n; i++)
	{
		for (j = i + 1; j <= n; j++)
		{
			M[i][i] = 0;
			M[i][j] = INFY;
		}
	}
 
	for (i = n; i > 0; i--)
	{
		for (j = i; j <= n; j++)
		{
			if (i == j)
				M[i][j] = 0;
			else
			{
				for (k = i; k < j; k++)
				{
					q = M[i][k] + M[k+1][j] + d[i-1] * d[k] * d[j];
					if (q < M[i][j])
					{
						M[i][j] = q;
						P[i][j] = k;
					}
				}
			}
		}
	}
}
 
int main()
{
	char input_str[100];
	int *d;
	int input, n, k;
 
	printf("input file name? ");
	scanf("%s", input_str);
 
	input_file = fopen(input_str, "r");
	if (input_file == NULL)
	{
		fprintf(stderr, "File %s not found\n", input_str);
		return 0;
	}
	output_file = fopen("output.txt", "w");
 
	fscanf(input_file, "%d", &input);
	n = input - 1;
	d = (int*) malloc(sizeof(int) * n);
	for (k = 0; k < n; k++)
	{
		if (fscanf(input_file, "%d", &d[k]) == -1)
		{
			d[k] = 0;
			n = k - 1;
			break;
		}
	}
 
	P = array_malloc(n);
 
	minmult(n, d);
 
	print_order(1, n);
 
	fclose(input_file);
	fclose(output_file);
 
	return 0;
}