Thread: K&R Exercise 1-14 - Looking for Critique

Hello all,

I'm currently working my way through the K&R book and am doing all the exercises as I come across them. This exercise asks me to write a program that prints out a histogram of the number of occurrences of each character in the input. I should note that on the x-axis, I list the ASCII codes of each character that appears in the file because it seemed the most consistent way to display the data while also including whitespace characters.

Here is my code:

Code:

/* Corresponding K&R section: 1.6 */

/* Counts frequencies of different characters in input */

#include <stdio.h>

#define NUM_CHARS 256

int main(void)
{
	int c = 0;
	int charFrequencies[NUM_CHARS] = {0};
	int maxFrequency = 0;

	/* -------------- Get Frequency Data --------------- */

	while((c = getchar()) != EOF)
		charFrequencies[c]++;
	
	/* --------------- Print Histogram ----------------- */

	/* NOTE: characters not appearing in the input will not
			 appear on the x-axis. To allow display of data
			 for non-printable characters, ASCII codes will
			 be used on the x-axis. */

	//Determine max frequency
	for(c = 0; c < NUM_CHARS; c++) 
	{
		if(charFrequencies[c] > maxFrequency)
			maxFrequency = charFrequencies[c];
	}
	
	//print y-axis and bars
	int i = 0;
	printf("\n\n");
	for(c = maxFrequency; c > 0; c--)
	{
		printf("%7d | ", c);
		for(i = 0; i < NUM_CHARS; i++)
		{
			if(charFrequencies[i] >= c)
				putchar('*');
			/* To align with the x-axis, only print
				a space if the character appears in
				the input */
			else if(charFrequencies[i] > 0)
				putchar(' '); 
		}
		putchar('\n');
	}

	//print x-axis

	//print dashes
	printf("        +-");
	for(i = 0; i < NUM_CHARS; i++)
	{
		if(charFrequencies[i] > 0)
			putchar('-');
	}
	putchar('\n');

	//print 100s digit of ASCII code
	printf("          ");
	for(i = 0; i < NUM_CHARS; i++)
	{
		if(charFrequencies[i] > 0)
			printf("%d", i / 100);
	}
	putchar('\n');

	//print 10s digit of ASCII code
	printf("          ");
	for(i = 0; i < NUM_CHARS; i++)
	{
		if(charFrequencies[i] > 0)
			printf("%d", (i % 100) / 10);
	}
	putchar('\n');

	//print 1s digit of ASCII code
	printf("          ");
	for(i = 0; i < NUM_CHARS; i++)
	{
		if(charFrequencies[i] > 0)
			printf("%d", (i % 100) % 10);
	}
	printf("\n\n");

	return 0;
}

I realize I am not using certain library functions that would help condense this code, but part of the challenge of the exercises is to implement a solution using only the components of the C language that I've been exposed to thus far. I'm mainly looking for comment on how well my solution scales with size of input, or if there are any known bad habits I'm indulging in.

Originally Posted by tabstop

Everything looks good, with the possible exception of turning "(i % 100) % 10" into just "i % 10".

Ohhh yeah, right you are. Not sure why I did that.

And thanks, CommonTater.

One other question. I've been defaulting to using putchar() if I only need a single character because I'm assuming it's faster than printf(), given that printf() has to check for and deal with format strings. Is that true?