Thread: string array stuck:(

Code:

scanf("%d",&num);
char no[num][50],name[num][50],sur[num][50];

This is very illegal - the reason why is because if you are declaring
an array in C, the dimensions need to be constant at compile
time (static memory allocation). If you don't know the dimensions
at compile time, malloc must be used (the dynamic in dynamic
memory allocation), you cannot do it in this manner. Should look
like this:

char no[10][50];

Also I'm getting errors for not having all variable declarations
at the start of the code block - i thought that this was changed
in the last C standard, but in case it wasn't and Visual Studio
is correct, move those lines directly under main(){...

Code:

printf("ID: ");
                      scanf("%s",&no[k][0]);

                      scanf("%s",&name[k][0]);

                      scanf("%s",&sur[k][0]);
                      k++;

very wrong as well - scanf takes the memory address of where
it is reading in to, but when dealing with strings it should just
take the name of the string it is reading into. what you have
set it up to do is read it into the kth row of the 0th column - a
single element within the array. because scanf does't do
bounds checking it keeps on reading into the 1st, 2nd columns
and so on. Normally this would crash your program but since
you declared arrays it is operating, but its not working correctly
to say the least. these lines of code should be as follows:

Code:

printf("ID: ");
                      scanf("%s", no[k]); /*notice no &?*/

Ideally you should be using fgets to read in strings anyway.

>>my compiler did not encountered any errors
That surprises me - dev-cpp should throw a fit at the array declarations - too lazy to try, but trust me - that code was very
wrong. It wouldn't complain about not declaring variables at
the start of main because you probably have the file saved
as .cpp - in C++ it would be legal, but as I said it may/may not
be legal in C.

Also, do you realise that your case 2 does its work in a very
ugly way - printf can print whole strings using %s - you don't
need to loop and print every character individually

On another note, your code indentation is very inconsistent and
it makes it very awkward to read. To that end, I've beautified it
and reposted it below. I've made the changes that make it work
properly and introduced some improvements.

Code:

#include <stdio.h>
#include <stdlib.h>
#define NUM 5

/*The above allows for arrayname [NUM] because the program knows NUM is always 5*/
/*This means that the compiler will create an array of 5*/

int main(void)
{
	int choice = 0;
	int k = 0, l = 0;
	int a1[NUM];

	float res = 0;

	char no[NUM][50], name[NUM][50], sur[NUM][50];

	printf("\n 1. Student registration.\n"
	" 2. List of course.\n"
	" 3. Enter final results.\n"
	" 4. Show average of final results.\n"
	" 5. Exit\n");

	while(choice!=5)
	{
		printf("your choice:");
		scanf("%d",&choice);
		switch(choice)
		{

		case 1:
			while(k<NUM)
			{
				printf("ID: ");
				scanf("%s",no[k]);
				printf("Name: ");
				scanf("%s",name[k]);
				printf("Surname: ");
				scanf("%s",sur[k]);
				k++;
			}
			break;

		case 2:
			printf("\n");
			printf("ID\tName\tSurname\n");
			
			do
			{
				printf("%s",no[l]);
				printf("\t");
				printf("%s",name[l]);
				printf("\t");
				printf("%s",sur[l]);
				printf("\n");
				l++;
			}while(l<NUM);	/*a for loop would work well here instead of do-while*/
			l = 0; /*output is scrambled if you choose case 2 twice - this repairs it*/
			break;

		case 3:
			for(l=0;l<NUM;l++)
			{
				printf("%s:",name[l]);
				scanf("%d",&a1[l]);
			}
			l = 0; /*as above*/
			break;

		case 4:
			for(k=0;k<NUM;k++)
			{
				res=res+a1[k];
			}
			k = 0; /*as above again*/
			
			res=res/(float)NUM;
			printf("average : %.2f\n",res);
			res = 0.0; /*again as above*/
			break;

		case 5:
			exit(1); /*this is a bit redundant since entering 5 should quit anyway*/
		}     
	}

	return 0;
}

Youre right about scanfs and my way of printing strings. Maybe I should blame my compiler there were no errors and when I erase the & and the column part of my multi arrays the program worked as well.
I mean:

Code:

scanf("%s",no[k]);//I understand its not the right way but "scanf("%s",&no[k][0]);" does the same job for my compiler?!...

Its also same for printf statements and

Code:

printf("%s\n",&no[l][0]);// and printf("%s\n",&no[l][0]); are same also or printing in a loop with "%c"...

I will install visual c and use it from now on. And also the code is compiled as .c file not .cpp!

For the memory allocation subject, the point why I had to declare arrays inside a switch and did not put static dimension is:
I MUST take the dimension as an input from the "user". And I seek a way to do it without using malloc() function. So I should really change my compiler program. Any suggestions?

note for Richie T: do not take it personal but may I kiss you for your efforts to teach me the proper C language(I really thank you and appreciate)!:P

note for everyone: I am straight, go away!

Originally Posted by Richie T

Code:

scanf("%d",&num);
char no[num][50],name[num][50],sur[num][50];

This is very illegal - the reason why is because if you are declaring
an array in C, the dimensions need to be constant at compile
time (static memory allocation). If you don't know the dimensions
at compile time, malloc must be used (the dynamic in dynamic
memory allocation), you cannot do it in this manner. Should look
like this:

char no[10][50];

Well actually, you can do it that way. C99 allows for mixing declarations throughout your code as well as arrays whose size aren't known until run time. However, there are very few (1?) fully C99 compliant compilers out there. Most of them that support C99 only support a few of its "features".


Quzah.

>>Maybe I should blame my compiler there were no errors

Visual didn't complain about the scanfs because compilers will only
do so much to avoid errors. There's nothing wrong with dev, its
just you might want to look into increasing the error checking it
does - look at compiler options. As Salem said, its built around the
gcc compiler so if you look at his compiler o/p you can see the
extra instructions that he passed to the compiler (-W -Wall -ansi -
pedantic -O2 ) - they might be a little different for dev but they
can be passed to it as well.

>>does the same job for my compiler?!...

As Salem regularly puts it "another person who learns works for
me C as opposed to standard C" (or something along those lines).
You need to understand why that code was wrong - also why
you shouldn't use scanf for reading in strings - its about as bad
as gets - I'd go so far as to say that its worse because it stops
reading at whitespace. As far as the printf goes - thats a matter
of choice - a stupid choice in my opinion since it involves
unnecessary loops, but hey its your program!

>>without using malloc()

you've probably seen quzah's statement - you will be pleased to
learn that the lastest code that I provided can very easily be
modified to use malloc. Its up to you. If you were going that
road, I would suggest practicing 2-d array allocation in a separate
program so you can get comfortable with the syntax involved -
then you will be able to adapt the program more easily as
opposed to messing with the current working code.

>>I had to declare arrays inside a switch

Well no. what I was saying was to do the allocation at the start
(ask for the dimensions at the start) and THEN enter the loop,
using only one memory allocation, and one deallocation - there was
no need to ask for the number of records inside in a loop where
repeated calls to malloc would be assigned to the same pointer -
each repeated time you choose that option that does the
allocation you trash the memory you allocated the previous time
(sorry if thats a little convoluted sounding).

>>I really thank you and appreciate

Your welcome - i help when I can, and it often results in improving
my own understanding of a concept, or learning something new
(as per quzah's post).