Frequencies of characters in a file

This is a discussion on Frequencies of characters in a file within the C Programming forums, part of the General Programming Boards category; Hi. I just wrote this program that's supposed to read from a file, count the frequency of each character, sort ...

  1. #1
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    Frequencies of characters in a file

    Hi. I just wrote this program that's supposed to read from a file, count the frequency of each character, sort them, then output any characters in a file along with their frequencies:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define FILEPATH_MAX FILENAME_MAX*15
    
    int main(int argc, char * argv[])
    {
    	char filePath[FILEPATH_MAX];
    	FILE *file;
    	int i, k, maxchar;
    	char charcount[256] = {0};				/* array to know how many of a specific character have been seen */
    	char charcount2[256] = {0};				/* for sorting */
    	char charcount2_identifiers[256] = {0};			/* for sorting (identifiers for characters in charcount2 */
    
    	if (argc == 2)
    		strcpy(filePath, argv[1]);
    	else
    	{
    		fputs("Wrong arguments. Press enter to terminate...", stderr);
    		getchar();
    		exit(EXIT_FAILURE);
    	}
    
    	if ((file = fopen(filePath, "rt")) == '\0')
    	{
    		fputs("Error opening file. Press enter to terminate...", stderr);
    		getchar();
    		exit(EXIT_FAILURE);
    	}
    	printf("File opened successfully\n");
    
    	/* start counting */
    	while ((i=fgetc(file)) != EOF)
    		++charcount[i];
    	
    	fclose(file);
    
    	/* sort */
    	for (i=0; i<256; i++)
    	{
    		for (k=0, maxchar=0; k<256; k++)
    			if (charcount[k] > maxchar)
    			{
    				maxchar = charcount[k];
    				charcount[k] = 0;
    				charcount2_identifiers[i] = k;
    			}
    
    		charcount2[i] = maxchar;
    	}
    
    
    
    	/* output results */
    	for (i=0; i<256; i++)
    	{
    		if (charcount2[i] != 0)
    		{
    			if (charcount2_identifiers[i] >= 33 && charcount2_identifiers[i] <= 126)
    				printf("&#37;c: %d\n", charcount2_identifiers[i], charcount2[i]);				/* print the identifier */
    			else
    				printf("0x%x: %d\n", charcount2_identifiers[i], charcount2[i]);
    		}
    	}
    
    	printf("Finished. Press enter to continue...");
    	getchar();
    
    	return 0;
    }
    The problem is, not all the characters in the file are output.
    E.g. I tried the following text in a file:
    UJTUQJ FQQ FWTZSI YMJ BTWQI QNPJ YT XTQAJ UZEEQJX
    when I run the program it does not display the letter J or its frequencey.

    I think the problem is in the sorting. I'm pretty sure the output part is right.

    Thanks,
    Last edited by Abda92; 12-13-2007 at 05:33 AM.

  2. #2
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    I'm a bit confused about your sorting algorithm. Have you tried printing the values BEFORE you sort them [so you print in alphabetical order]?

    Edit: I see the problem. You are setting you charcount[i] = 0 whenever you find something that is greater than the current maxchar - but you don't know yet if this is actually the HIGHEST SO FAR. You need to just remember the position of the highest one, _THEN_ set it to zero at the same time as you set the charcount2[i] to maxchar.

    --
    Mats
    Last edited by matsp; 12-13-2007 at 05:39 AM.
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
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    yes. It worked fine. I'm sorry about the sorting algorithm, it's the first time I've every tried writing one. Here's the code without the sorting (outputs in alphabetical order):
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    #define FILEPATH_MAX FILENAME_MAX*15
    
    int main(int argc, char * argv[])
    {
    	char filePath[FILEPATH_MAX];
    	FILE *file;
    	int i, k, maxchar;
    	char charcount[256] = {0};				/* array to know how many of a specific character have been seen */
    	char charcount2[256] = {0};				/* for sorting */
    	char charcount2_identifiers[256] = {0};			/* for sorting (identifiers for characters in charcount2 */
    
    	if (argc == 2)
    		strcpy(filePath, argv[1]);
    	else
    	{
    		fputs("Wrong arguments. Press enter to terminate...", stderr);
    		getchar();
    		exit(EXIT_FAILURE);
    	}
    
    	if ((file = fopen(filePath, "rt")) == '\0')
    	{
    		fputs("Error opening file. Press enter to terminate...", stderr);
    		getchar();
    		exit(EXIT_FAILURE);
    	}
    	printf("File opened successfully\n");
    
    	/* start counting */
    	while ((i=fgetc(file)) != EOF)
    		++charcount[i];
    	
    	fclose(file);
    
    
    	/* output results */
    	for (i=0; i<256; i++)
    	{
    		if (charcount[i] != 0)
    		{
    			if (i >= 33 && i <= 126)
    				printf("&#37;c: %d\n", i, charcount[i]);				/* print the identifier */
    			else
    				printf("0x%x: %d\n", i, charcount[i]);
    		}
    	}
    
    	printf("Finished. Press enter to continue...");
    	getchar();
    
    	return 0;
    }

  4. #4
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    Did you see my edit?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  5. #5
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    Oh sorry, I just saw it. I'll try implementing it now (shouldn't take any time).
    but do you have any better sorting algorithms that I can use (just a simple one)? or does mine seem OK?

    EDIT: I just implemented it now. but I don't like the look of this statement:
    Code:
    /* sort */
    	for (i=0; i<256; i++)
    	{
    		for (k=0, maxchar=0; k<256; k++)
    			if (charcount[k] > maxchar)
    			{
    				maxchar = charcount[k];
    				charcount2_identifiers[i] = k;
    			}
    		
    		charcount[charcount2_identifiers[i]] = 0;
    		charcount2[i] = maxchar;
    	}
    Is it illegal in C? because it works completely fine.
    Last edited by Abda92; 12-13-2007 at 05:58 AM.

  6. #6
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    That's perfectly legal, if a bit complex.

    I would probably just store maxchar's "k" in a temp variable, and set both charcount2_identifier and the charcount using that temp variable.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  7. #7
    Super Moderator VirtualAce's Avatar
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    Are you allowed to use C++? Moreso the std library?

  8. #8
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    Well, I'm allowed to but I don't know how (and I'd rather not).
    I got it working fine now with the following code:
    Code:
    /* sort */
    	for (i=0; i<256; i++)
    	{
    		for (k=0, maxchar=0; k<256; k++)
    			if (charcount[k] > maxchar)
    			{
    				maxchar = charcount[k];
    				maxchar_identifier = k;
    			}
    		
    		
    		charcount2_identifiers[i] = maxchar_identifier;
    		charcount[maxchar_identifier] = 0;
    		charcount2[i] = maxchar;
    	}

  9. #9
    Super Moderator VirtualAce's Avatar
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    Ok that's fine. std::map has a very nice feature for this but I'm glad you got it working.

  10. #10
    Frequently Quite Prolix dwks's Avatar
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    This is the C forum, and as I don't see anything C++-ish about that code -- it looks like plain, vanilla C -- you probably shouldn't be recommending std::map.

    Code:
    if ((file = fopen(filePath, "rt")) == '\0')
    '\0' is usually used as a character. When you're dealing with pointers, which is what fopen() returns, it's standard practise to use NULL instead -- or just plain 0. Or even
    Code:
    if (!(file = fopen(filePath, "rt")))
    Code:
    			if (i >= 33 && i <= 126)
    				printf("&#37;c: %d\n", i, charcount[i]);
    Consider isprint() from <ctype.h>. It's more portable and easier on the eyes, too.

    Instead of using the "magic number" 256 everywhere, you could use UCHAR_MAX from <limits.h>. Or not; 256 is pretty common.

    Rather than declare a large array with FILENAME_MAX*15 elements, which still might not be enough, you could just declare filePath as a pointer and have it point to argv[1]. That wouldn't work if you wanted to add support for fgets()-ing the filename from the user at some point in the future, however.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


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  11. #11
    Chinese pâté foxman's Avatar
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    Indeed, UCHAR_MAX is defined as 255 and not 256.

    I know you knew it DWKS (or maybe was it a small moment of inattention), but i just wanted to point out that if he puts UCHAR_MAX instead of 256, he'll have to use the "<=" operator instead of the "<".

  12. #12
    Frequently Quite Prolix dwks's Avatar
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    Of course, I forgot about that. Maybe something like this, then:
    Code:
    #define CHARS (UCHAR_MAX + 1)
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
    Projects: codeform, xuni, atlantis, nort, etc.

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