Write a function named indexOf that returns the index of a particular value in an array of integers.
The function is passed the array, its length, and the target value as parameters, and it should return the index of the first occurrence of the target value in the array.
If the value is not in the array, return -1.
For example, if an array called list stores the following values:
int list[] = {42, 7, -9, 14, 8, 39, 42, 8, 19, 0};
Then the call indexOf(list, 10, 8) should return 4 because the index of the first occurrence of value 8 in the array is at index 4.
The call indexOf(list, 10, 2) should return -1 because value 2 is not in the array.
