Why does N keep changing its value?

[jaumzaum]

In the program below, when I input a number bigger than 99 for variable N, N changes its value during the execution. When I input a small number, it does not!

Why is that?

#include "stdafx.h"

int N, K, MAPA[101][101];

int main() {
	scanf("%i %i", &N, &K);
	printf("%i\n\n", N);
	for (int a = 1; a < N+2; a++) {
		for (int b = 1; b < N+2; b++) {
			MAPA[a][b] = 0;
		}
	}
	printf("%i", N );
	return 1;
} 

EXAMPLES:
IN
200 200
OUT
200

0


IN
4 4
OUT
4

4

[clanmjc]

you are out of the bounds of that array with the large numbers, you define the size as 101.

[jaumzaum]

But if I input 100 100 I get the same output:

100

0

So, it does not make sense.

[yasar11732]

you are out of the bounds of that array with the large numbers, you define the size as 101.

So would this mean that memory location of N is next to the last element of the MAPA array and that is causing it to be set to 0?

[Mathhead200]

100 + 2 == 102 (Out of bounds)
An array with size 101 has indexes 0-100...

[clanmjc]

But if I input 100 100 I get the same output:

That is because 100 + 2 = 102

for (int a = 1; a < N+2; a++)

resulting in... after last iteration of the for loop
a = 101

Remeber c++ is 0 based index, so a size of 101 elements are indexed 0-100. 101 is out of bounds

[clanmjc]

So would this mean that memory location of N is next to the last element of the MAPA array and that is causing it to be set to 0?

Yes, it is assigning 0 at the memory location that happens to be where N is at. By moving the declaration of N somewhere else this wouldn't happen, but you still have the out of bounds problem.

[Mathhead200]

Only on some systems (particularly little-endian.) Don't rely on this behavior! Accessing (dereferencing and/or changing the value of) memory that's out of bounds is unsupported and causes undefined behavior.