Overwriting nodeid when allocating nodeid++ in 2D array while moving

Question

I'm trying to allocate updated nodeid values to new array elements, but everytime I do so, I overwrite my nodeid value with the initial value of the array element in which I allocate nodeid. Here's what I'm talking about:

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

int motion (int nodeid, int row, int column, int direction) {

    nodeid = field [row][column];

    while (((row < (LENGTH - 1))&&(row > 0))||((column < (WIDTH - 1))&&(column > 0))){
        if (direction == 0){
            nodeid++;

            nodeid = field [row][column + 1];
            column++;
        }
        else if (direction == 1){
            nodeid++;
            nodeid = field [row][column - 1];
            column--;
        }
        else if (direction == 2) {
            nodeid++;
            nodeid = field [row - 1][column];
            row--;
        }
        else if (direction == 3) {
            nodeid++;
            nodeid = field [row + 1][column];
            row++;
        }
    }

    return 0;
}

and here's my custom header file, motion.h:

#define LENGTH 18
#define WIDTH 12
#define SAMPLES 8
enum direction {Right, Left, Up, Down};
int field [LENGTH][WIDTH];
int column;
int row;
int nodeid;
int direction;
int motion (int nodeid, int row, int column, int direction);
int print_field (int field[][ WIDTH ], int row, int column);

and my source code, main.c:

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

int main() {

int samples;
int i;
int j;
int k;

printf ("How many samples do you want?\n");
scanf ("%d", &samples);

for (i = 0; i < samples; i++){
       printf ("Indicate nodeid, row, column and direction\n");
       scanf ("%d %d %d %d", &nodeid, &row, &column, &direction);
for(j = 0; j < LENGTH; j++)
{
       for(k = 0; k < WIDTH; k++){
       field[j][k] = 0;
}
}
motion (nodeid, row, column, direction);
printf ("\n%d", print_field(field, row, column));
}

return 0;
}
~

As you can see, code such as nodeid = field [row][column + 1] overwrites nodeid++ (according to my knowledge). How do I properly allocate nodeid without overwriting it?

UPDATE: Good news and bad news. Good news is that it displays my answers now. Bad news:

Indicate nodeid, row, column and direction
_____________________________
|0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000|
|0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000|
|0.0000.0000.0000.0000.0000.0000.0000.0000.0000.000|
_____________________________

As you can see, all of my results are 0 inside the bar along with dots here and there.

This is the code for my print_Field function:

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

int print_field(int field[][ WIDTH ], int row, int column){

int i;
int j;
int k;
int t;

for ( k = 0; k < WIDTH * 6; k++){
    printf("_");
}

printf ("\n");

for ( i = 0; i < LENGTH; i++){
printf ("|");

for (j = 0; j < WIDTH; j++){
printf( "%.3f", field [i][j]) ;
printf (" ");
}

printf ("\n");

for ( i = 0; i < LENGTH; i++){
printf ("|");

for (j = 0; j < WIDTH; j++){
printf( "%.3f", field [i][j]) ;
printf (" ");
}
printf ("\b|");
printf ("\n");
}
for (t = 0; t < WIDTH * 6; t++){

printf("_");
}
printf ("\n");
return 0;
}

After much tinkering, I got this:

 ________________________________________________________________________

 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 |0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000|
 ________________________________________________________________________

Apparently, there's still something iin my motion.c code that's preventing the non-zero numbers from displaying.

Answer 1

You have your assignment backwards. Instead of

 nodeid = field [row][column + 1];

try

 field [row][column + 1] = nodeid;

Also, you should use your enumeration constants (Right, Left, etc.) in your motion function. And you should define column, row, nodeid, and direction inside main, not globably.

So, I'd rewrite it like this:

int motion (int nodeid, int row, int column, int direction) {

    field [row][column] = nodeid;

    while (row < LENGTH - 1 && row > 0 && column < WIDTH - 1 && column > 0){
        if (direction == Right)
            field[row][++column] = ++nodeid;
        else if (direction == Left)
            field[row][--column] = ++nodeid;
        else if (direction == Up)
            field[--row][column] = ++nodeid;
        else if (direction == Down)
            field[++row][column] = ++nodeid;
    }

    return 0;
}