trying to read integer with scanf in array

Question

I made some code to compare temperature of the week.

I made two functions, one to write to the array, other one is to calculate average temp. It compiles without errors. As soon as I enter my first number the app crashes and I get this error in the stdio.h lib :

Exception thrown at 0x533C742E (ucrtbased.dll) in 7.3.exe: 0xC0000005: Access violation writing location 0xCCCCCCCC.

I made a similar exercise without functions and it was working perfect. Hope you guys can help me out. Here is my code

#include <stdio.h>
#define MAX 7
#define _NO_CRT_STDIO_INLINE
void read(int);
float gem(int);

int main(void)
{
    float x = 0;
    int temp[MAX];
    read(temp[MAX]);
    x = gem(temp[MAX]);
    printf("%f", x);
}

void read(int k[MAX])
{
    for (int i = 1; i < 8; i++)
    {
        printf("geef de temp voor dag %d ", i);
        scanf_s("%d%*c", &k[i-1]);
    }
}

float gem(int y[MAX])
{
    int som = 0;
    float gem = 0;
    for (int i = 0; i < 8; i++)
    {
        som += y[i - 1];
        gem = som / 7;
        return gem;
    }
}

How and why did you think `void read(int)` would be equal to `void read(int k[MAX])`? Perhaps you should take a few steps back, and [read a couple of good beginners books](http://stackoverflow.com/questions/562303/the-definitive-c-book-guide-and-list). — Some programmer dude, Oct 25 '17 at 10:14
unrelated : `gem = som / 7; return gem;` --> `gem = som / 7.; return gem;` (or `gem = (double)som / MAX; return gem;`) and move after for-loop. — BLUEPIXY, Oct 25 '17 at 10:21

score 2 · Answer 1 · answered Oct 25 '17 at 10:13

When in doubt, check the data type!!

In your code, the function call

  read(temp[MAX]);   //trying to pass an int type

is wrong. The function accepts an int *.

You need to pass the pointer to the beginning of the array, like

  read(temp);

That said, temp[MAX] is already off-by-one, causing undefined behavior.

Also, your loop controller variable usage is bit odd. You can simply use like

  for (int i = 0; i < MAX; i++)

and then, use i as the iterator (indexing).

score 0 · Answer 2 · answered Oct 25 '17 at 10:54

Generally,Parameters are always passed by value in C. Therefore, in the above code, value of read(temp[MAX]); is not modified using the function. So how do we modify the value of a local variable of a function inside another function. Pointer is the solution to such problems. Using pointers, we can modify a local variable of a function inside another function. We only get the effect of pass by reference using pointers.

trying to read integer with scanf in array

2 Answers2