exercise13.c

// C Primer Plus
// Chapter 13 Exercise 13:

// Do Programming Exercise 12, but use variable-length arrays (VLAs) instead of
// standard arrays.

// Note: use data.txt as input file to test this program.

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <stdbool.h>

int main(int argc, char *argv[])
{
	FILE *fp;
	int ch;
	int rows = 0, cols = 0, lastrow_cols;
	bool first_line;

	if (argc != 3)
	{
		printf("Usage: %s <data file> <image file>\n", argv[0]);
		exit(EXIT_FAILURE);
	}

	// open data file
	if ((fp = fopen(argv[1], "r")) == NULL)
	{
		fprintf(stderr, "Could not open file %s.\n", argv[1]);
		exit(EXIT_FAILURE);
	}

	// this passage of code counts the number of columns in each row
	// and compares them for consistency, exiting with an error if they're
	// not all equal
	first_line = true;
	while ((ch = getc(fp)) != EOF && isdigit(ch))
	{	

		cols = 1;
		while ((ch = getc(fp)) != EOF && ch != '\n')
			if (isdigit(ch))
				cols++;
		if (first_line)
		{
			first_line = false;
		}
		else
		{
			if (cols != lastrow_cols)
			{
				fprintf(stderr, "Invalid data file: unequal number of columns in rows.\n");
				exit(EXIT_FAILURE);
			}
		}
		lastrow_cols = cols;
	}
	if (cols == 0)
	{
		fprintf(stderr, "Invalid data file.\n");
		exit(EXIT_FAILURE);
	}

	// this passage counts the number of rows
	rewind(fp);
	while ((ch = getc(fp)) != EOF)
		if (ch == '\n')
			rows++;

	// with the number of rows and columns counted, the data and img arrays
	// can be allocated dynamically
	int data[rows][cols];
	char img[rows][cols + 1];

	// read ints from file
	rewind(fp);
	for (int i = 0; i < rows; i++)
		for (int j = 0; j < cols; j++)
			if (fscanf(fp, "%d", *(data + i) + j) != 1)
			{
				fprintf(stderr, "Invalid data file.\n");
				exit(EXIT_FAILURE);
			}
	fclose(fp); // done with data file

	// convert ints to characters
	for (int i = 0; i < rows; i++)
	{	
		int j;
		for (j = 0; j < cols; j++)
		{
			switch (data[i][j])
			{
				case(0):
					ch = ' ';
					break;
				case(1):
					ch = '.';
					break;
				case(2):
					ch = '\'';
					break;
				case(3):
					ch = ':';
					break;
				case(4):
					ch = '~';
					break;
				case(5):
					ch = '*';
					break;
				case(6):
					ch = '=';
					break;
				case(7):
					ch = '}';
					break;
				case(8):
					ch = '&';
					break;
				case(9):
					ch = '#';
					break;
				default:
					fprintf(stderr, "Error: int out of bounds.\n");
					exit(EXIT_FAILURE);
			}
			img[i][j] = ch;
		}
		img[i][j] = '\0'; // j = cols here
	}

	// open image file
	if ((fp = fopen(argv[2], "w")) == NULL)
	{
		fprintf(stderr, "Could not open file %s.\n", argv[2]);
		exit(EXIT_FAILURE);
	}

	for (int i = 0; i < rows; i++)
	{
		// print to console and file
		puts(img[i]);
		fprintf(fp, "%s\n", img[i]);
	}
	fclose(fp);

	return 0;
}