[array]: Statement, I don't understand

[tbessi]

My arrays are in 6 positions? right

why notes[60] don't failed?
and why notes[66] run failed?

IDE: NetBeans 7.3.1

#include <iostream>
using namespace std;
int main(void) {
    float notes[6];
    int chapters[6];
    short Class[6];
    notes[60]=100.0;
    chapters[10]=19;
    Class[149]=149;
    
   /*
    notes[66]=12.5; --- run failed
    chapters[72]=19 -- run failed
    Class[150]=150; -- run failed
   */
   cout << notes[60]<<endl;
   cout << chapters[10]<<endl;
   cout << Class[149]<<endl;
   return 0;
} 

[MrHutch]

Accessing out of bounds array subscripts results in undefined behaviour. Sometimes it may fail, sometimes it may not. In any event, it should be avoided.