"ferror" tests "scanf" input

I tried to enter error data in next program but it can't recognize the error. Once I entered numeric data, and next time entered string data but the program made no reaction:

#include <iostream>
#include <cstdio>
#include <cstdlib>

using namespace std;

int main(void)
{
    int i;

    scanf("%d",&i);

    if(ferror(stdin))
        printf("Error is ocurred!");
}

Don't assume what a function does. Read it's documentation.

https://www.cplusplus.com/reference/cstdio/ferror/

int ferror ( FILE * stream );

Check error indicator

Checks if the error indicator associated with stream is set, returning a value different from zero if it is.

This indicator is generally set by a previous operation on the stream that failed, and is cleared by a call to clearerr, rewind or freopen.

So this depends on if scanf has set the error indicator, which it does not in this situation.

Instead, use this:

if(scanf("%d",&i) != 1) {
    // Error code

Oh, and don't use use namespace std Why is "using namespace std;" considered bad practice?