Thread: Difficulty With Defining an Array

Basically I'm attempting to write this program but it refuses to compile, giving the error message:

Code:

Compiling and linking file: Project2.c
D:\C PROJECT\PROJECT2.C(24) : error 185 - A constant expression is required here
*** Compilation failed
Compilation failed

The program is as follows:

Code:

/*This program was written by Chris Tayler. Work started on 4/11/05*/

/*The purpose of this program is to calculate the gradient, y-intercept and the uncertainty in the gradient for a line
of best fit determined by a series of points input by the user of the program. The line of best fit is drawn using the
"least squares fitting" method.*/

#include<stdio.h>
#include<math.h>

int main (void)

{

	int N; /*Declares N to be an interger*/     
        
	printf("Please enter the number of (x,y) coordinates you recorded: ");

    scanf("%d",&N); /*Determines value for N (user specified)*/

    printf("\nThe number of values you recorded is: %d\n\n", N); /*Prints value of N*/ 
   
	int x, y; /*Declares x and y to be intergers*/

	int results[N][2]; /*(attempts to) declare an array with N rows and 2 columns*/
  	
    printf("Enter your %d pairs of values in the form (x,y), pressing return after each pair\n\n", N);
  
	return 0;
    
}

The error message is referring to line 24 which is:

Code:

int results[N][2]; /*Declares an array with N rows and 2 columns using the pointer *n*/

Any help on this one is appreciated, i'm still having issues with C!

Thanks for the help Sahil, i think i understand how the #define command works but i'm still having difficulty assigning the value of n using scanf. This is that section of code as it stands at the moment:

Code:

#include <stdio.h>
#define N 100

int main(void)

{printf("Please enter the number of (x,y) coordinates you recorded: ");

    scanf("%d",&N); /*Determines value for N (user specified)*/

    printf("\nThe number of values you recorded is: %d\n\n", N); /*Prints value of N*/ 
  }
 
{

	int arr[MAX][2];
	int n=10;
	int i,j;

	for(i=0;i<n;i++)   /*User defined for size*/
	{
		for(j=0;j<2;j++)
		{
		  scanf("%d %d", i, j, &arr[i], &arr[j]);
		}
	}

	return 0;
}

This code returns the following error message:

Code:

Compiling and linking file: tester.c
F:\C PROJECT\TESTER.C(8) : error 99 - & Requires an lvalue operand
F:\C PROJECT\TESTER.C(13) : error 199 - '{' found where a type specifier was expected
F:\C PROJECT\TESTER.C(28) : fatal 233 - Compilation abandoned
Compilation failed

The other issue with the code in this form is that the values to be input into the array will need to be floats but the compiler didn't like it when i tried to use scanf with %f. I think this is down to the fact that the array needs to be defined using intergers? How do i get around this?

Again any help is appreciated, i've got a help class tomorrow but i'd like to make some progress before then.

Thanks again people.

That's whats causing my problem. I need to have an array that uses a user defined number of columns. The rest of the program is easy enough its just getting that bit sorted that's causing issues!

I also think that my syntax is wrong for using scanf to get data into my array? I'm currently trying to use:

Code:

	int n=10;
	int i,j;

	for(i=0;i<n;i++)   /*User defined for size*/
	{
		for(j=0;j<2;j++)
		{
		  scanf("%d %d", i, j, &arr[i], &arr[j]);
		}

But it seems to me that the %d's should really be %f's so that the values input into the array can be decimals? Could anyone confirm/correct me on this one?

Thanks guys, i'm getting there (albeit slowly)!

Originally Posted by cbastard

So, as already told above.Use a c99 compiler or allocate memory dynamically using malloc.

Unfortunatley i'm restricted to using Salford Plato3 as my compiler so that's not an option and our course hasn't covered dynamic memory allocation so i'm thinking there must be a way to do it using the #define command...?

Originally Posted by cbastard

You want to store four integer values so increase the no. of %d's by two.Since you have two dimensional array,so you should give whole address like &a[x][y]

So this would give me

Code:

{	for(x=0;x<N;x++)  

	{	for(y=0;y<2;y++)
		
scanf("%d, %d,", x, y, &arr[x][y]);

}
  
         }

as my syntax?

Originally Posted by cbastard

yes,Because int cant store decimal values.

The problem i'm having with this is that the position in the array cannot be a float so if the input from the user is going to define both the recorded value and the position in the array then neither %f or %d will work?

This is beginning to drive me crazy! Thanks again guys.

After some fiddling about i've managed to get it to work, thanks guys!

The code i used is:

Code:

#include <stdio.h>
#define MAXSIZE 100

void main()
	
{	int i, size;
		
int A[MAXSIZE], B[MAXSIZE];
		
{
	printf("How many (x,y) values did you collect?: ");
	scanf("%d",&size);
}
		while (size < 1 || size > MAXSIZE);
        		
				printf("\nPlease enter the %d x-values:\n\n", size);
		        for (i = 0; i < size; i++)         /* reads values for x */
    		    scanf ("%d", &A[i]);
	
					printf("\nPlease enter the %d y-values\n\n", size);
					for (i = 0; i < size; i++)         /* reads values for y */
  		   			scanf ("%d", &B[i]);
		
						for (i = 0; i < size; i++)        
    		    		printf("\nThe data points you entered: (%d,%d)", A[i], B[i]); /* displays (x,y) cooridinates */
                        printf("\n");

                      
	}

Happy now, its probably not the most elegant soloution but at least it works properly!

Thanks again.