Array gets modified not int when called in a function

Question

When I run this program-

#include <stdio.h>
void inc( int num[], int n)
{
  int i;
  n++;
  for(i=0;i<10;i++)
    num[i]++;
}

int main()
{
  int arr[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 0};
  int a=2;
  inc (arr, a);
  int i; 
  for(i=0;i<10;i++)
    printf("%d  ", arr[i]); 
  printf("\n%d  ", a);
return 0;
}

I get the output-

2  3  4  5  6  7  8  9  10  1                                                                                                                  
2

I understand why the int is unchanged but I don't understand why the array is getting changed since I have not used pointers to call the array. I know that the function will make a different copy of n and assign n=a and all changes will happen to n only and a will be unchanged. Why the array is getting changed?

The array *degrades to* a pointer when used like this. It is not (and can not) be copied during the function call. — Jonathon Reinhart, Nov 24 '18 at 05:58
Functionally `void inc( int num[], int n)` is the same as `void inc( int *num, int n)` — Support Ukraine, Nov 24 '18 at 06:13
When you pass an array to a function, you are using pointers, whether you know it or not. — Jonathan Leffler, Nov 24 '18 at 06:28
*I know that the function will make a different copy [...]* – the 2nd parameter will be copied, yes. But arrays don't have copy semantic in C and C++. Just try `int foo[5]; int bar[5]; foo = bar;` — Swordfish, Nov 24 '18 at 07:14
you are passing array pointer not array in calling inc(arr, n) — Elbek, Nov 24 '18 at 08:14

score 0 · Answer 1 · edited Nov 24 '18 at 07:16

0

In C, except for a few cases, an array name decays (=gets implicitly converted) to a pointer to its first element.

This

void inc(int num[], int n)

is exactly same as this:

void inc(int *num, int n)

edited Nov 24 '18 at 07:16

Swordfish

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answered Nov 24 '18 at 06:53

H.S.

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[C11 Standard - 6.3.2.1 Other Operands - Lvalues, arrays, and function designators(p3)](http://port70.net/~nsz/c/c11/n1570.html#6.3.2.1p3) – David C. Rankin Nov 24 '18 at 08:16

Array gets modified not int when called in a function

1 Answers1