Thread: Lvalue error? Whats that?

Hey guys thanks very much for your input. My prof does brackets like

Code:

if (x) {
...
}

but I see a lot of code on these forums look like the following so I adapt them that way (plus its easier to make sure your syntax is correct)

Code:

if (x)
{
...
}

BUT, I have one more issue guys which I would really love your help on. After resubstituting the corrections in my program doesn't display the sorted words...at all...the program comes to a halt with this code ;

(really sorry for the eye sore, don't have time to tidy it up)

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char **p;
char size[20];
char buff[21];
char temp[21];
int N;
int j,i,k,l,m,d,s,a,b;

int main()
{
	do{
		d=0;
		printf("How many words would you like: ");
		fflush(stdout);
		for(j=0; j<20; j++)
		 {
		      size[j]=fgetc(stdin);
		      if (size[j]=='\n')
		      {
		        size[j]='\0';
		        break;
		      }
		 }/* end j-loop */
			if (j==0){
				printf("That input is empty.\n");
				d=1;

			}
		    if (j==20) {
		      printf("That input is too long.\n");
		      while(fgetc(stdin)!='\n');
		      d=1;
		  }
}while(d!=0);


	printf("You want %d words.\n", atoi(size));

	N=atoi(size);
	p=(char**)malloc(N*sizeof(char*));
		if (p==NULL)
		{
			printf("Memory error");
			exit(0);
		}
	for (i=0; i<N; i++)
		p[i]=(char*)malloc(21*sizeof(char));
		if (p[i]==NULL)
		{
			printf("Memory error");
			exit(0);
		}
	printf("Do not enter more than 20 characters.\n");

	for(k=0; k<N; k++)
	{
		A:printf("Enter a word: ");
		fflush(stdout);
		for(m=0; m<21; m++)
		{
		      buff[m]=(char)fgetc(stdin);
		      if (buff[m]=='\n')
		      {
		        buff[m]='\0';
		        break;
		      }
		 }

		    if (m>=21)
		    {
		    	printf("Word is more than 20 characters.\n");
		      	while(fgetc(stdin)!='\n');
      			goto A;
			}
			if (m==0)
			{
				printf("That input is empty\n");
				goto A;
			}
		strcpy(p[k],buff);
	}
	printf("\n");
	printf("Your unsorted list of Names:\n");
	k=0;
	for(k=0; k<N; k++)
		printf("%s\n",p[k]);


	for (a=N; a>0; a--)
	{
		for (b=0; b<a; b++)
		{
			if(strcmp(p[b],p[b+1])>0)
			{
				strcpy(temp,p[b]);
                                strcpy(p[b],p[b+1]);
                                strcpy(p[b+1], temp);
			}
		}

	}
	printf("\n");
	printf("Your sorted list of Names:\n");
	k=0;
	for(k=0; k<N; k++)
		printf("%s\n",p[k]);



return 0;
}

The program just...stops at "Your sorted output is :" and you have to CTRL + break to get out of it.

When N (the number of words they want) is 0 -zero- the "sorted" output is a smiley face...lol does that point out what I am doing wrong?

The code provided by my professor was;

Code:

		        if(strcmp(p[b],p[b+1])>0)
			{
				temp=p[b];
                                p[b]=p[b+1];
                                p[b+1]=temp;
			}

Basically he illustrated it as changing the location of the pointers (which makes sence) however using that code gives me Lvalue issues(which I don't know what that error means).

See

http://en.wikipedia.org/wiki/Indent_style

The first code snippet is an example of K&R, the second of Allman. Allman has the advantage of treating the opening and closing braces symmetrically, but K&R saves vertical screen space. I've toyed with the idea of using Pico style (described in the link) which both treats the braces symmetrically and saves screen space, but unfortunately almost no one else seems to use it.

Originally Posted by Elysia

temp is not a pointer, however. If temp was a pointer, then your professor's code would work.

So i used

Code:

char *temp
...
temp=(char*)malloc(21*sizeof(char));
		if (p==NULL)
		{
			printf("Memory error");
			exit(0);
		}
...

for (a=N; a>0; a--)
	{
		for (b=0; b<a; b++)
		{
			if(strcmp(p[b],p[b+1])>0)
			{
				temp=p[b];
                                p[b]=p[b+1];
                                p[b+1]=temp;
			}
		}

	}

And I still have the same issue of a halt in my program,

Originally Posted by swoopy

>temp=(char*)malloc(21*sizeof(char));
You don't need this line since you're just swapping pointers.

>for (a=N; a>0; a--)
This should probably be:
for (a=N-1; a>0; a--)
Otherwise you wind up running off the end of the array in the b loop (b+1).

Yes! It works! thank you so much man! I'll have to just think through that correction though so I understand what it was doing

Originally Posted by Elysia

Pico style is bad, horrible and poor. It absolutely destroys readability of code.
And what for? Saving two lines of code? I do not see the point in that.

Objectively, it's no less readable than K&R or Allman. In all three, to the human reader, scope is determined by a statement's horizontal offset. If the braces were invisible, the code could be read almost as easily. The three styles essentially just generate different amounts of vertical white space.

Originally Posted by Elysia

This is not true to many. The brackets help define the beginning and end of a block. Especially when there's no good indentation.
And when using a style like that, you hide the bracket is obscure places, making them hard to find.
And what's the deal with saving two lines of vertical space!? Saving horizontal space is far more important.

In essence, it hurts readability.

I don't think anyone who indents their code properly should care about whether the braces can be found easily in unindented code. And if the code is indented properly, in any style, each scope can be identified by its horizontal offset, so one doesn't even need to see the braces (only the compiler needs that, since it ignores the whitespace). I don't understand why you think saving horizontal space is more important - if lines are long enough that they start wrapping around, far more horizontal space can be recovered by reducing each scope's horizontal offset (by going from 4 spaces to 2, say) than by putting braces on separate lines. On the other hand, the vertical space saved by the more compact styles can be considerable, since it's one or two lines saved for each scope, and each scope may only be a few lines to begin with.