scanf 2d array size C

Question

I've tried to make custom array size by:

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

int main()
{
    int x;
    int y;

    printf("Array size:");
    scanf("%d %d", &x, &y);

    int kancelar[x][y];
    int i;
    int q;

    for (q = 0; q < x; q++)
        for (i = 0; i < y; i++)
            kancelar[q][i] = getchar();

    for (q = 0; q < x; q++)
        for (i = 0; i < y; i++)
            putchar(kancelar[q][i]);

    return 0;
}

But no luck, values were wrong. I'm using C,

What do you mean by 'values are wrong'? What values did you get and what values did you expect to get? — ForceBru, Feb 06 '16 at 13:48
@DanielKubica, it's not a problem, it's a _requirement_. But still, this should be a minimal code example, not some huge code — ForceBru, Feb 06 '16 at 13:50
You should dynamically allocate memory, using `malloc` functions. — WhatsUp, Feb 06 '16 at 13:51
http://pastebin.com/QysV9jaf I can write unlimited characters, and if the array is [2][3] it'll ask only for 1 line. for example. — Daniel Kubica, Feb 06 '16 at 13:52
`scanf("%d %d",&x,&y);` --> `scanf("%d %d%*c",&x,&y);` , show your input. — BLUEPIXY, Feb 06 '16 at 13:59
@DanielKubica Show your input. and Explain the _values were wrong_. — BLUEPIXY, Feb 06 '16 at 14:20
you declare a 2d array of ints but read characters, is this really what you want? — AndersK, Feb 06 '16 at 14:27
so by first loop i don't add characters? Idk what version i'm using but it's most probably C89 — Daniel Kubica, Feb 06 '16 at 14:44

score 1 · Answer 1 · edited Feb 06 '16 at 14:23

1

You are getting messed up by the newlines present in the input buffer by the press of the Enter key after each input. You need to consume the newline each time before going for the getchar().

A simple solution may look like

printf("Array size:");
scanf("%d %d%*c",&x,&y);  //eat up the newline
int kancelar[x][y];
int i;
int q;
for(q = 0;q < x;q++)
{
    for(i = 0;i < y;i++ )
    {
        kancelar[q][i] = getchar();
        getchar(); //eat up newline
    }

}

edited Feb 06 '16 at 14:23

Spikatrix

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answered Feb 06 '16 at 14:08

Sourav Ghosh

133,132
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thanks, but now it gave me 5 lines of input when wanted 3x4 array, and output is still wrong – Daniel Kubica Feb 06 '16 at 14:31

Yousuf Azad · Answer 2 · 2016-02-06T14:50:38.130

0

scanf("%d %d",&x,&y);
int kancelar[x][y];

You cannot create an array with variable values, you can do this with only constant values. So to create a custom array you need to allocate memory for you array dynamically

I have taken this code from this link : LINK

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

int main()
{
    int r, c;
    scanf("%d %d",&r,&c);

    // allocating memory
    int *arr = (int *)malloc(r * c * sizeof(int));

    int i, j, count = 0;
    // giving them default values
    for (i = 0; i <  r; i++)
      for (j = 0; j < c; j++)
         *(arr + i*c + j) = ++count;

    // printing the values 
    for (i = 0; i <  r; i++)
      for (j = 0; j < c; j++)
         printf("%d ", *(arr + i*c + j));

   // free memory
   free(arr);

   return 0;
}

Check out the link as they show more than one ways to achieve this

edited Feb 06 '16 at 14:50

answered Feb 06 '16 at 13:59

Yousuf Azad

414
1
7
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3

yes you can, it is called VLA i.e. if you have a C99 compiler (or later) https://en.wikipedia.org/wiki/Variable-length_array – AndersK Feb 06 '16 at 14:05
1

1)Remove the cast from `malloc` as it is unneccessary 2)Declare `r` and `c` 3)`free` the allocated memory – Spikatrix Feb 06 '16 at 14:24
@AndersK. Did not know that. – Yousuf Azad Feb 06 '16 at 14:48
@CoolGuy Thanks! about #1 malloc returns void pointer, don't we need to cast it first? [malloc reference](http://www.cplusplus.com/reference/cstdlib/malloc/) – Yousuf Azad Feb 06 '16 at 14:53
@sami1592 `void*` is automatically converted. Read [Do I cast the result of malloc?](http://stackoverflow.com/q/605845/3049655) – Spikatrix Feb 06 '16 at 15:04

scanf 2d array size C

2 Answers2