Passing 2D-array as argument into function

Question

The program's objective is to manipulate data inside a 2D-array.

int main(void)
{
    int array[500][500];
    int x0, y0;
    if ( input(array, &x0, &y0)==0 )
        return 1;

    return 0;
}
int input( int array, int *x0, int *y0 ) {
    int x = 0;
    int y = 0;
    int err = 0;
    char c;
    printf("Enter sizes:\n");
    if ( scanf("%d %d", x0, y0)!=2 || *x0<=0 || *y0<=0 || *x0>500 || *y0>500 ) {
        printf("Invalid input.\n");
        return 0;
    }
    while ( y < *y0 ) { 
        x = 0;
        while ( x < *x0 ) { //reading entries in x coordinate
            c = getchar();

            switch(c) {
            case 'o' : array[y][x] = 1; break;
            case '.' : array[y][x] = 0; break;
            case '!' : array[y][x] = 2; break;
            default : err = 1; break;
            }
            x++;
        }
        if( x!=*x0 )
            err=1;
        y++; //move to another "line"
    }
    if (y!=*y0)
        err=1;
    if (err==1) {
        printf("Invalid input.\n");
        return 0;
    }

    return 1;
}

The program will firstly get dimensions of the array and then get one of the three letters: o, ! or . for example:

3 3

ooo

.!o

...

The problem is that my function doesn't accept its arguments: input(array, &x0, &y0) which leads to me being unable to write into that array in the switch. In the former case passing argument 1 of 'input' makes integer from pointer without a cast while in the latter subscripted value is neither array nor pointer nor vector.

My previous program used a 1D array and this way of passing arrays into functions worked.

So how should I pass my array as an argument into functions? Thanks in advance.

chqrlie · Accepted Answer · 2015-12-05 23:40:12Z

1

Move the code for the main function after that for the input function so the prototype for input is known when compiling main.

Change the prototype for input to this:

int input(int array[500][500], int *x0, int *y0) {

There are other issues with your code. For instance you do not correctly handle the line feed entered after each matrix row.

edited Dec 5, 2015 at 23:40

answered Dec 5, 2015 at 23:27

chqrlie

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10 Comments

Hichigaya Hachiman Over a year ago

Didn't wanna write prototype since the code-part was already long. Anyway, this works. Although, why don't I have to write the size of the array in a 1D-array? Also do you have idea why the last iteration of while ( y<*y0 ) increments the y twice?

chqrlie Over a year ago

Arrays decay into pointers when passed to a function. In the case of a 2D array, a pointer to an array of arrays is passed, the second 500 is ignored and could be elided. I don't see how y would get increment twice. What makes you think that?

Hichigaya Hachiman Over a year ago

I printed y after increment. For 3 3 ooo 1 ooo 2 3

chqrlie Over a year ago

The line feed after the 3 3 is read by the first getchar() so the first entry is not read correctly. The same happens for each subsequent line feed is you do not enter all matrix values on a single line. The code that prints y is not what you posted, there might be other problems.

chqrlie Over a year ago

It hurts me to recommend using scanf, but scanf will ignore white space characters, including the linefeeds. So you can write char s[2]; if (scanf("%1s", s) == 1) { c = *s; }

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