Pointers trouble

I am really stuck here so just looking for some hints and advice. I dont know how to explain what my assignment is without actually posting what I have. So far I am only through the first bullet. I dont know where to go from there. I have read through the entire chapter again and I just dont know what parameters to pass to function drawImage and how to write the other two required functions. So, this is everything I have, I am not asking anyone to do this assignment for me, I simply want some pointers, no pun intended:

The Assignment
The objective of this program is to create an image (25 x 25) with a square of a user-defined size centered on the image.
The program will:
• Ask the user what size of square to draw (Maximum size of a side is 23, make sure to error check this entry)
• Call the function drawImage, included in the drawImage.h header file
• Call a function to print the image to the screen, using an * to demarcate the square
• Call a function that uses a pair of pointers to search through the image to determine where the edge of the square is located. This function should generate a new image that has only the outline of the square.
• Lastly recall the print function to print the image with the outline.

Submit the code as hw7-2.c

Hints:

1. Use these function prototypes
void printImage(int image[]);
void edgeDetection(int image[], int edge[]);

2. If using a one-dimension array to define a two-dimension image the following is a useful method for incrementing through the array: r + c*SIZE. Where r is the current row, c the current column and SIZE is the length of a row.

Given header file

Code:

---

/******************************************************************
 *                                                                *
 * Programmer:                                  *
 * Name: drawImage                                                *
 * Function: Draws a square onto the center of a canvas          *
 * Input: 1-D Array, width of array, length of square,            *
 * whether the square side is even or odd length                  *
 *    line and give a description of what it is>                *
 * Output: An array with 1s where the square is on the image      *
 *                                                                *
 ******************************************************************/



//Function to draw a square centered within an image
void drawImage( int image[], int size, int side, int even)
{
        int r, c;

        //loop through the image setting the appropriate pixels to "white" if the square is present
        for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                {
                        if ((size/2 - side/2) > r || (size/2 + side/2 - even) < r )
                        {
                                //Leaves the value of the array as it is since no part of the image appears in this row
                        }
                        else if( (size/2 - side/2) > c || (size/2 + side/2 - even) < c )
                        {
                                //Leaves the value of the array as it is since no part of the image appears in these columns
                        }
                        else
                        {
                                image[r+c*size] = 1;
                        }
                }
        }
}

---

This all I have so far, dont know what to do next, I do know pointers are necessary:

Code:

---

#include <stdio.h>
#include "drawImage.h"

/*function prototypes*/
void printImage(int image[]);
void edgeDetection(int image[], int edge[]);

/*function main begins program execution*/
int main (){
       
        int SIZE;
       
        printf("Please enter the size of the square you would like to draw" 
                        "\n(maximum size is 23):");  /*print statement*/
        scanf("%d",&SIZE);

       
        if(SIZE>23){
                printf("The size of the square cannot be larger than 23, please start again\n");
               
                return 0;
        } /*end if*/

        return 0; /*indicate program ended successfully*/
} /*end function main*/

---

first off, I just need help with what to pass on to drawImage. It requires 4 inputs. All I have in function main is the length of the square. I dont know what to pass for the other three parameters.

You have to create the array to begin with:

Code:

---

int array[25 * 25];

---

Here's a start:

Code:

---

// clear array
int i;
for(i = 0; i < 25 * 25; i ++)
    array[i] = 0;
even = (side & 1);
drawImage(array, 25, side, even);

---

The assignment is confusing and written badly to begin with, so don't feel too bad. Most C programming teachers couldn't cut it at a real job, this is an obvious example.

Quote:

---

Originally Posted by joed

The assignment is confusing and written badly to begin with, so don't feel too bad. Most C programming teachers couldn't cut it at a real job, this is an obvious example.

---

lol. Thanks. I thought I was the only one who had no idea what they were telling me to do. Ill give your stuff a try. Do I actually put "even" in drawImage()?

Quote:

---

Originally Posted by joed

You have to create the array to begin with:

Code:

---

int array[25 * 25];

---

Here's a start:

Code:

---

// clear array
int i;
for(i = 0; i < 25 * 25; i ++)
    array[i] = 0;
even = (side & 1);
drawImage(array, 25, side, even);

---

The assignment is confusing and written badly to begin with, so don't feel too bad. Most C programming teachers couldn't cut it at a real job, this is an obvious example.

---

I dont understand the assignment for even. So is that not if the side is an even number? Or is it a typo? Could you just explain it for me please.

>even = (side & 1)

if side is even ,then even is set to 0.
if side is odd,then even is set to 1.

Quote:

---

Originally Posted by qqqqxxxx

>even = (side & 1)

if side is even ,then even is set to 0.
if side is odd,then even is set to 1.

---

Oh, I didnt know that. Thanks.

Okay, so the way Im understanding this is that the drawImage function is creating a square of 1's right? So in my printImage function I can just tell it to change 1's to *? If so, I am only passing the array to printImage per the assignment. So how will that work?

EDIT: Or can I set this function equal to an array or something? then just pass that on? maybe pointers involved?

EDIT: That wont work because drawImage doesnt return a value.

>void edgeDetection(int image[], int edge[]);

what do u think this is for?

Quote:

---

Originally Posted by qqqqxxxx

>void edgeDetection(int image[], int edge[]);

what do u think this is for?

---

Im working on the printImage function. It doesnt require the use of this function. Or maybe I dont know what youre getting at.

I know I need to pass an array to printImage.

EDIT: Wait, passing the array to drawImage actually changes the array right? So if I pass it to printImage and just go through the array changing all the 1's to * that should work?

u dont have to change the 1's to *.
where ever u find a 1 ,note that position,
and print an * on the corresponding position on the screen.

since the array is 1d u will have to convert the 1d array index value to a 2d screenposition coordinate.

Quote:

---

Originally Posted by qqqqxxxx

u dont have to change the 1's to *.
where ever u find a 1 ,note that position,
and print an * on the corresponding position on the screen.

since the array is 1d u will have to convert the 1d array index value to a 2d screenposition coordinate.

---

Okay, I think I understand what youre saying, but how would I go about doing that?

EDIT:
something like this?

Code:

---

for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                { 
                        if(image[r+c*size] = 1){

---

but what do I put in the if statement.

>If using a one-dimension array to define a two-dimension image the following is a useful method for incrementing through the array: r + c*SIZE. Where r is the current row, c the current column and SIZE is the length of a row.

that was suggested as a hint.

>if(image[r+c*size] = 1)

image[r+c*size]==1

Quote:

---

Originally Posted by qqqqxxxx

>if(image[r+c*size] = 1)

image[r+c*size]==1

---

whoops.

try:
gotoxy(r,c);
printf("*");

does it have anything to do with storing the memory location?

Quote:

---

Originally Posted by qqqqxxxx

try:
gotoxy(r,c);
printf("*");

---

While that may work, I dont think I can really use it because I havent learned anything like that. But i'll look through the book quick and see if it is anywhere, then I could use it.

EDIT: actually I just remembered at the beginning of the semester they said we could not use goto statements.

gotoxy can be used for positioning the cursor at (r,c)
but it is non standard.

Quote:

---

Originally Posted by qqqqxxxx

gotoxy can be used for positioning the cursor at (r,c)
but it is non standard.

---

do you think there is any other way to do it?

This is what I got, I know its wrong, but is there something I could change to make it work?

Code:

---

int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

        for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                { 
                        if(image[r+c*size] == 1){
                                printf("*");
                        }
                }
        }

---

I just wanted to get this straight because Im not so sure. The drawImage function is creating a square of 1s right? Because when I try out the program with the function I added, it just ends after asking for the size of square I want. Basically I think its implying that no element in the array equals 1 (in my printImage function).

EDIT: if this helps this is all I have:

Code:

---

#include <stdio.h>
#include "drawImage.h"

/*function prototypes*/
void printImage(int image[]);
void edgeDetection(int image[], int edge[]);

/*function main begins program execution*/
int main (){
       
        int side;
        int square[625];
        int i, even;

        printf("Please enter the size of the square you would like to draw" 
                        "\n(maximum size is 23):");  /*print statement*/
        scanf("%d",&side);

        for(i = 0; i < 625; i ++){
                square[i] = 0;
        }

        even = (side & 1);

        drawImage(square, 25, side, even);

        printImage(square);

       
        if(side>23){
                printf("The size of the square cannot be larger than 23, please start again\n");
               
                return 0;
        } /*end if*/

        return 0; /*indicate program ended successfully*/
} /*end function main*/

void printImage(int image[]){
        int r, c;
        int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

        for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                { 
                        if(image[r+c*size] == 1){
                                printf("*");
                        }
                }
        }
}

---

Code:

---

int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

---

so when u use this size in the rest of your program,it doesnt traverse through the whole array.
>printf("*");

u wont get a square,because u have to set the cursor at the correct position first.

Quote:

---

Originally Posted by qqqqxxxx

Code:

---

int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

---

so when u use this size in the rest of your program,it doesnt traverse through the whole array.

---

Well here I am just trying to get the length of the square. I was thinking all I needed was the length of a side. Am I wrong?

the problem is u have still not understood the assignment well and neither have i.
go through the drawimage function.
make sure u understand what is going on inside it.

then think of the printimage function.

so,
image array defines the canvas.
and the square is loacted in the center of the canvas.

Quote:

---

Originally Posted by qqqqxxxx

the problem is u have still not understood the assignment well.
go through the drawimage function.
make sure u understand what is going on inside it.

then think of the printimage function.

so,
image array defines the canvas.
and the square is loacted in the center of the canvas.

---

This is true, I am not really understanding the assignment well. I think I understood the part about the canvas and the square being in the center of the canvas, but Im just not understanding how it really works and how my functions should work. I guess Ill just give it some more thought. Thanks for your help though.

int size=0;

for(r=0;r<25;r++){
if(image[r]==1){
size++;
}
}

Code:

---

---

sorry, this will give u the side,but u already know the side.

Quote:

---

Originally Posted by qqqqxxxx

int size=0;

for(r=0;r<25;r++){
if(image[r]==1){
size++;
}
}

Code:

---

---

sorry, this will give u the side,but u already know the side.

---

but the side hasnt been passed on to this function. so this is needed right?

and i tried running your program,the printimage function is working.

Quote:

---

Originally Posted by qqqqxxxx

and run your program put a printf after the size calculation,see if u r gettin the side.

---

well, no, the program is just ending after the user prompt to enter the desired size. This is why I was trying to understand drawImage better.

Quote:

---

Originally Posted by qqqqxxxx

and i tried running your program,the printimage function is working.

---

Its working? When I enter the size I want, the program just ends without any warnings or anything. But, it doesnt print anything.

Code:

---

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

void gotoxy(int x, int y)
{
  COORD coord;
  coord.X = x;
  coord.Y = y;
  SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), coord);
}



void drawImage( int image[], int size, int side, int even)
{
        int r, c;

        //loop through the image setting the appropriate pixels to "white" if the square is present
        for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                {
                        if ((size/2 - side/2) > r || (size/2 + side/2 - even) < r )
                        {
                                //Leaves the value of the array as it is since no part of the image appears in this row
                        }
                        else if( (size/2 - side/2) > c || (size/2 + side/2 - even) < c )
                        {
                                //Leaves the value of the array as it is since no part of the image appears in these columns
                        }
                        else
                        {
                                image[r+c*size] = 1;
                        }
                }
        }
}





printimage(int image[],int size)
{
int r,c;
  for (r = 0; r < size; r++)
        {

                for (c = 0; c < size; c++)
                {    if((image[r+c*size])==1)
                        {gotoxy(r,c);
                        printf("*");}
                }
        }
}











main(){
int r;
int image[25*25];
for(r=0;r<625;r++)
 {
  image[r]=0;
 }


int size =25;
int side =10;
int even =1;
drawImage(image,size,side,even);
printimage(image,size);

}

---

i ran this on my machine,u can skip the gotoxy part,but it should print out a line of *'s without the gotoxy.

hmmm... well I am gonna have to work on this a little, Im still not getting anything. But, I have to study for an exam I have tommorrow, or today I guess.

Thanks for your help qqqxxxx.

Code:

---

int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

---

and i went through your code again,this is why u r not gettin anything

here u r just checking the first row of the canvas,the very top row so u will get size=0 even after the for loop.

but the square is located on center.

and u want size to be 25,and u r trying to get the side length.

Code:

---

even = !(side & 1);

---

sorry!

Quote:

---

Originally Posted by qqqqxxxx

Code:

---

int size=0;

        for(r=0;r<25;r++){
                if(image[r]==1){
                        size++;
                }
        }

---

and i went through your code again,this is why u r not gettin anything

here u r just checking the first row of the canvas,the very top row so u will get size=0 even after the for loop.

but the square is located on center.

and u want size to be 25,and u r trying to get the side length.

---

I cant think of anyway to get the length of the side of the square without actually passing that to the function (which I am not supposed to do per the assignment).

EDIT: I think I thought of something but I dont know how to do it. Each element in the array is a different memory location which are in consecutive order? So if it goes through the memory locations, dereferences them, and starts counting when it hits a 1, then stops when it hits a zero, that should work. Could somebody walk me through how I could go about doing that? I know it involves pointers.

Code:

---

int r=0,side=0;
while(image[r]!=1)r++;
while(image[r]==1){r++;side++;}

---

Quote:

---

Originally Posted by qqqqxxxx

Code:

---

int r=0,side=0;
while(image[r]!=1)r++;
while(image[r]==1){r++;side++;}

---

---

but that wouldnt go through just the first line would it?

nope first it finds a 1.

Im thinking the best way to do this, if possible, is to create a pointer. Go through the each element of the array and dereference it. If it is a 0 leave it. If it is a 1 change it to *. After all the point of this assignment is to practice pointers.

Is this possible?

EDIT: maybe im just thinking of the next function, which would require me to find the edge of the square. In that case I would need to check adjacent memory locations , thus requiring a pointer.

This is what he posted on the site as a hint yesterday but thats for the second function:

Use two pointers to search through the array, and deference these pointers to obtain the value for adjacent points in the array. Check to see if the dereferenced value for the two pointers is unequal, and then place a 1 in the edge[] array corresponding to the location that the pointer of higher value points to.
The purpose of this assignment is to practice dereferencing pointers!

image[1] is the same as *(image +1);

arrays and pointers have alot in common.

Code:

---

int im[10];
im[10]=10;
int *p=im;
printf("%d",*(p+10));

---