Thread: Character Arrays - 1.9 in K&R. need help

Hi everyone,

I'm stuck on section 1.9 in the K&R book.

My main problem is that I copied the code from the book verbatim and it's not printing the string for me. I'm not getting any errors when I compile. When I run the program I type in some lines and hit control-D to trigger EOF, and it doesn't print the string from the 'longest' array - printf("%s", longest);



other confusion with arrays as function arguments:

in the 'copy' function, to[] and from[] are in the function prototype, but their length is never defined, as opposed to line[] and longest[], which are specified in main()

also it is confusing to me how getline() has (char line[], int maxline) in its prototype, but calls (char s[], and int lim) in its definition. Where as copy() uses the same arguments for its prototype and its definition.


many thanks for any help!
Nick

Post your code ... be sure to use code tags.

When I run the program I type in some lines and hit control-D to trigger EOF, and it doesn't print the string from the 'longest' array - printf("%s", longest);

CTRL D might not be EOF on your computer OS. When I typed it into a command prompt in windows, I got an error. If you're on windows you want CTRL Z.

in the 'copy' function, to[] and from[] are in the function prototype, but their length is never defined, as opposed to line[] and longest[], which are specified in main()

also it is confusing to me how getline() has (char line[], int maxline) in its prototype, but calls (char s[], and int lim) in its definition. Where as copy() uses the same arguments for its prototype and its definition.

Yeah, parameter names can be different in the prototype and the definition. It's legal C. I suspect that the authors wanted to simply demonstrate this, but don't be confused. As you know now, having the names be different isn't helpful.

Originally Posted by NickDesigner

...also it is confusing to me how getline() has (char line[], int maxline) in its prototype, but calls (char s[], and int lim) in its definition. Where as copy() uses the same arguments for its prototype and its definition.

Parameter names are optional in a function prototype; getline() prototype can be just written as:

Code:

int getline(char, int)

Only constraint is that the prototype has to agree with the definition and uses of the function.

Originally Posted by Matticus

Post your code ... be sure to use code tags.

Especially since we don't all have the K&R book...

Here is the code:

Code:

#include <stdio.h>
#define MAXLINE 1000

int getline(char line[], int maxline);
void copy(char to[], char from[]);

/*prints longest input line */
int main()
{

	int len;			/* current line length */
	int max;			/* maximum length seen so far */
	char line[MAXLINE];		/* current input line */
	char longest[MAXLINE];	/* longest line saved here */

	max = 0;
	while ((len = getline(line, MAXLINE)) > 0)
		if (len > max)
		{
			max = len;
			copy(longest, line);
		}
	if (max > 0)	/* there was a line */
		printf("%s", longest);
	return 0;
}

/* getline: read a line into s, return length */
int getline(char s[], int lim)
{
	int c, i;
	
	for (i=0; i<lim-1 && (c=getchar()) !=EOF && c!='\n'; ++i)
		s[i] = c;
	if (c == '\n')
	{
		s[i] = c;
		++i;
	}
	s[i] = '\0';
	return i;
}

/* copy:  copy 'from' into 'to'; assume to is big enough */
void copy(char to[], char from[])
{
	int i;
	
	while((to[i] = from[i]) != '\0')
		++i;
}

Thank you so much! It was in fact that missing i = 0; in copy() that was the problem. I'm running on a Mac so control-D is the EOF command. Now that I made that fix it works, but the funny thing is my compiler didn't give me an error before. :/

I have also just recently discovered the Steve Summit site, and I've been using this site which has the answers to the exercises, though I've found some of them hard to understand due to lack of explanation of the code. For example, their solution to Exercise 1-17 uses pointers even though we haven't seen them yet in the book.

The C Programming Language Answers To Exercises

Originally Posted by NickDesigner

The C Programming Language Answers To Exercises

C'mon now... no cheating allowed.

That would be great - I'm using Xcode 3.

Wow I didn't realize there were such advanced options for compiler warnings. Thanks you for the article, I will dive into this right away.

Another quick question about simple programming logic:

As far as I am understanding, a program runs through its code in a certain order, so when it reaches a called function it doesn't move on until that function finishes executing and possibly returns a value. So in the case of the code above, when user input is involved, does the program sort of halt at (c = getchar()) and only continue through the for loop when getchar() returns a value and sets it equal to c?