Addressing multidimensional arrays in C

Question

what is the problem? i think there's no logic problem or compile error

but the loop suddenly stopped after looping 16 times...

is this gcc compiler's error? i almost freaked out ...

like there's no compile error that pops up but doesn't work,,,

thanks in advance : ) sorry for the editing question

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#define RIGHT    0
#define DOWN     1
#define LEFT     2
#define UP       3

int main()
{
    int x,y;
    scanf("%d %d", &x, &y);     

    int **arr;
    arr = (int**)malloc(sizeof(int*)*x);
    for(int i = 0; i < x; i++)  arr[i] = (int*)malloc(sizeof(int) * y );

    int x_ = 0, y_ = 0;         
    int MAX_x = x-1;    
    int MAX_y = y-1;                
    int MIN_x = 0;                  
    int MIN_y = 0;              
    int direction = RIGHT;          
    int num   = 0;

    while(true)
    {

        arr[x_][y_] = num++;

        printf("%d", num);
        //printf("%d", arr[x_][y_]);

        switch ( direction )
        {

        case RIGHT:
            if( y_ == MAX_y )
            {
                direction = DOWN; MIN_x ++; x_++;
            }
            else
            {
                y_++;
            }
            break;

        case DOWN:
            if( x_ == MAX_x )
            {
                direction = LEFT; MAX_y --; y_--;
            }
            else
            {
                x_++;
            }
            break;

        case LEFT:
            if( y_ == MIN_y )
            {
                direction = UP; MAX_x --; x_++;
            }
            else
            {
                y_--;
            }
            break;

        case UP: 
            if( x_ == MIN_x )
            {
                direction = RIGHT; MIN_y ++;  y_++;
            }
            else
            {
                x_++;
            }
            break;

        default : break;
        }


        if(num == x * y )
            break;
    }


    for(int i = 0; i < x; i ++)
    {
        for(int j = 0; j < y; j ++ )
        {
            printf("%3d", arr[i][j]);
        }
        printf("\n");
    }
}

Welcome to Stack Overflow! Please take the [tour] and visit the [help] to get the most out of this site. — CJ Dennis, Aug 10 '18 at 11:59
I'd recommend using more descriptive variable names, perhaps something like `numberOfRows`, `numberOfColumns`, `rowIndex`, or `columnIndex` instead of `x_`, `y_`, `x`, `y` — jrh, Aug 10 '18 at 12:00
Read this question and its answers: https://stackoverflow.com/questions/42094465/correctly-allocating-multi-dimensional-arrays — Andrew Henle, Aug 10 '18 at 12:00
Just do `int arr[x][y];` and avoid all the complication of malloc — M.M, Aug 10 '18 at 12:55
thank you guys i will try and try to add more none code writing — JaeJu, Aug 11 '18 at 00:46
What is the output you expect with this program? Loop will stop when the condition if(num == x * y ) is met. There's nothing sudden about this. — P.W, Aug 14 '18 at 05:54

score -1 · Accepted Answer · answered Aug 10 '18 at 13:54

-1

In your case LEFT you want to decrement x_, not increment it. change your x_++ to x_--.

In your case UP you also want to decrement, so change that x_++ to x_--.

I think your confusion here is that moving up requires a decrement, not an increment.

answered Aug 10 '18 at 13:54

Sean

101
5

Addressing multidimensional arrays in C

1 Answers1