The reason why sizeof (ARR) / sizeof (arr[0]) is used in the function to calculate the length of the array is incorrect

Problem description

sizeof() The function is to find the memory space occupied by the array （ It's not the length ）. When using this method to find the length of an array in a function , As the array is passed into the function as a function parameter, it will “ degeneration ” For the pointer , Therefore, it will lead to sizeof(arr) What we get is the memory space size of a pointer , Not the memory space of the array –> Thus, the calculated length is wrong

// Enter a number to see if there is this number in the series  
#include <stdio.h>
int main ()
{
    
	int a[]={
    1,2,3,4,34,455,23,4,7,1,9,6,8,};
	int i=0,x,logic=0,n;
	int fun(int x,int a[],int logic);
	printf(" Please enter a number ：\n");
	scanf("%d",&x);
	n=fun(x,a,logic);
	if(n==-1)
	printf(" The number was not found in the sequence \n");
	else{
    
	printf(" Enter this number, which is the number %d position \n",n);
}
	printf("%d\n",n);
	return 0;
 } 
 	int fun(int x,int a[],int logic)
{
    
	 logic=-1;
	 int i;
 	for (i=0;i<sizeof(a)/sizeof(a[0]);i++)
	{
    
		if(x==a[i])
		{
    
		logic=i;
		break;
	    }  
	    
	}
	return logic;
}

---

Solution ：

int main() {
    
	int a[] = {
     1,2,3,4,34,455,4,7,1,98,6 };
	int len = sizeof(a) / sizeof(a[0]);
	int i = 0, x, logic = 0, n;
	int fun(int x, int  len, int a[], int logic);
	printf("please input a num: \n");
	scanf("%d", &x);
	n = fun(x, len, a, logic);
	if (n == -1)
		printf("not find");
	else {
    
		printf("at %d ", n);
	}
	return 0;

}
int fun(int x, int len,int a[], int logic) {
    
	logic = -1;
	
	for (int i = 0; i < len; i++) {
    

		if (x == a[i]) {
    
			logic = i;
			break;
		}
	}
	printf("%d\n", logic);
	return logic;
	
}