what if we increase the value of x in for loop while working with array

Question

for example this is the program:
#include <iostream>
using namespace std;
int main(){
int myArr[5];
for(int x=0; x<=4; x++) {
myArr[x] = 42;
cout << x << ": " << myArr[x] << endl;
}
return 0; }

which gives an output:
0: 42
1: 42
2: 42
3: 42
4: 42

but if change x<6 in for loop it gives output:
0: 42
1: 42
2: 42
3: 42
4: 42
42: -2045

please explain this -2045

Answer 1

This is an error. You are telling the compiler to go beyond the allocated memory space for myArr. Since myArr only allocates memory for five integers, by saying myArr[5], you are making an error. You should adjust your loops to account for the size of your array. In this case, it should look like this:

int myArr[5];
int arrSize = sizeof(myArr)/sizeof(int);

for (int i = 0; i < arrSize; i++) {
myArr[i] = 42;
cout << i << ": " << myArr[i] << endl;
}

Or you can use a for-each loop:

int x = 0;
for (auto i : myArr) {
i = 42;
cout << x++ << ": " << i << endl;
}

Answer 2

you are accessing the memory area which falls outside of the array boundry. The size of your array is 5 but with i < 6, you are trying to read the value at location myArr[5], can contain garbage data or valid data of other programs running on your system. In current case, the value @ location myArr[5] is -2045 and that is what is printed.