Thread: Double Pointer Trouble

The following programme is supposed to use pointers totype double variables to accept 10 numbers, sort them, print them.

Code:

/* D14Ex7.c - programme to use pointers to type double to accept 10 numbers *
 * from the user, sort them and print them to the screen. */

#include <stdio.h>

double *ptr[10];

int main ( void )
{
        int cnt;
        printf("\t\t\t====You must enter 10 numbers====\n");
        for (cnt = 0; cnt < 10; cnt++)
        {
                printf("\nEnter number %d: ", cnt);
                scanf("%lf", ptr[cnt]);
        }

        for (cnt = 0; cnt < 10; cnt++)
        {
                printf("\n%f", *ptr[cnt]);
        }
        return 0;
}

Sorry if it's not formatted well, I'm using a text-based brwser
I'll check later to see if I need to repost the code. The poblem is that after entering a first number, the programme generates a `segmentation fault' error and goes to the shell.
Any suggestions?

You have to allocate memory for each of the 10 slots in the array. Look up malloc( ).

Sorry if it's not formatted well, I'm using a text-based brwser

That's no excuse. Use code tags. (IE: Read that nice little thread that tells you how to do them.)

[code]
...your code here...
[/code]

Quzah.

OK. There's the CODE tag.

Anyhow, Thanx XSquare, That problem is solved now.

However, another one's come up:
Could someone tell me what's wrong with this code:

Code:

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

void sort(double *ptr[]);

int main ( void )
{
        double *ptr[10];
        int cnt;
        for (cnt = 0; cnt < 25; cnt++)
                printf("\n");

        printf("\t\t\t\t=========You must enter 10 numbers=========\n");
        for (cnt = 0; cnt < 10; cnt++)
        {
                ptr[cnt] = malloc(10*(sizeof(double)));
        }

        for (cnt = 0; cnt < 15; cnt++)
                printf("\n");

        for (cnt = 0; cnt < 10; cnt++)
        {
                printf("\nEnter number %d: ", cnt+1);
                scanf("%lf", ptr[cnt]);
        }

        sort(ptr);
        printf("\n");
        return 0;
}

void sort(double *ptr[10])
{
        int a;
        double x;

        printf("<<SORTING>>");
        for(a = 0; a < 10; a++)
        {
                if(*ptr[a] < *ptr[a+1])
                {
                        x = *ptr[a+1];
                        *ptr[a+1] = *ptr[a];
                        *ptr[a] = x;
                }
        }

        printf("\n");
        for(a = 0; a < 10; a++)
        {
                printf("\t%f\n", *ptr[a]);
        }
        printf("\n");

}

Any help?
Thanx

>>ptr[cnt] = malloc(10*(sizeof(double)));
Should be just sizeof( double ). You only want 1 double per slot, not 10.

Since you're using bubble sort, you should also have 2 for loops in your sort function. Otherwise it won't get sorted.

Pseudocode:

Code:

for each pass from 1 to n
    for each element from 1 to n - 1
        if the current element is less than the number after it
            swap them
        end if
    next element
next pass

Also, you aren't free( )ing your memory that you malloc( )ed.

1) In your loop, you realize that you are allocating 10 doubles for each pass through the loop, right? I hope that was intended.

2) Your next loop only enters ten numbers. One into each element of the loop. You have 90 elements unused.

Fix the above first.

Additionally, don't just say "What's wrong with my code." No one here wants to read hundreds of lines of code looking for some obscure problem because you haven't taken the time to simply provide:

"My program does[n't do] this."
"My program [should|does] do this."
"I am getting [this error|no errors]."

If you want help, you need to provide as much information as possible.

[edit]Beat me to it.[/edit]

Quzah.

You quote your original problem, and yet you post two seperate code instances. In the first example, you didn't allocate any memory. That's your first problem.

In your second example, you didn't allocate memory correctly. You still haven't fixed that problem. There's nothing more to help, short of doing all your work for you. There are easily enough code examples and comments for you to resolve the problem.

Quzah.