我可以将int传递给C中的void函数吗？

Question

I'm trying to use functions to let the user enter a n by n square matrix and print it out.

The function for entering a matrix is: ucitajmatricu

And to print it out: ispisimatricu

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

void ucitajmatricu(int);
void ispisimatricu(int);

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

  ucitajmatricu(n);
  ispisimatricu(n);

  return 0;
}

void ucitajmatricu(int n) {
  int i, j;

  int MAT[n][n];

  for (i = 0; i < n; i++) {
    for (j = 0; j < n; j++) {
      scanf("%d", & MAT[i][j]);
    }
  }
  printf("\n");

  return;
}

void ispisimatricu(int n) {
  int i, j, MAT[n][n];
  for (i = 0; i < n; i++) {
    for (j = 0; j < n; j++) {
      printf("%d\t", MAT[i][j]);
    }
    printf("\n");
  }

  return;
}

Example input: 3

1 2 3
4 5 6
7 8 9

Example output:

1 2 3
4 5 6
7 8 9

Actual output:

1 2 3
4 5 6
7 48 0

Answer 1

void ucitajmatricu(int n) {
...
int MAT[n][n];

...

void ispisimatricu(int n) {
int i, j, MAT[n][n];

The two declarations of MAT[][] are in different functions - they do not retain their value and the fact they have the same name has no importance.

Declare MAT[][] once, outside a function. And, BTW, this problem seems to have nothing to do with the title of the question.

EDIT after comment

The program seems to work-only-partly because in the first call the values are read and stored in a local array (in the stack). The second called function has a similar (if not identical) stack frame, so the frame declared and instantiated in the second call is overlaid to the previous one, by chance, almost 100%. The second function appears to mantain a large part of the values, but this is just luck (or unluck...). If, between the two calls, there were other calls to other functions, the stack would get more corrupted (well, overwritten) and the effect of work-only-partly would decrease.

The type of bug in the OP program is nasty because the stack "luckily" mantains part of the values, but "unluckily" this fact masks out the real problem: local variables disappear after the function exits.

Answer 2

To elaborate on the above answer, when you declare a variable in a function you are declaring it on the stack.

You could declare and initialize globally but that would be different than what it appears you want to do. Easier in some ways since depending on stack memory but more rigid.

To use your current implementation initialize your matrix by allocating on the heap instead. Use calloc() to allocate and zero the space. Then when you return, return the pointer to your matrix. Downside is more memory management required.