When this is run, we sometimes get the following puzzling output: Array elements 9 and 10 are out of order. Even more puzzling, sometimes we don’t get this output. Why?

Question

Suppose we want an array to satisfy the condition,
```
a[0] <= a[1] <= a[2] <= ...
```
And suppose this code is written to implement a test of this condition

```
#include using namespace std; int main() { double array[10] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; // assume the array is filled somehow. for(int i=0; i < 10; i++) if (array[i] > array[i+1]) cout << "Array elements " << i << " and "
<< i + 1 << " are out of order.\n";
}
When this is run, we sometimes get the following puzzling output:
Array elements 9 and 10 are out of order.
Even more puzzling, sometimes we don’t get this output.
Why?

```

Answer 1

There is an index out of range. When index i has value 9, i + 1 is 10, so a[i+1], which is the same thing as a[10] causes an illegal access. The loop should stop with one fewer iterations. To correct this code, replace the for loop header with for(int i=0; i < 9; i++)