TestComplete's C#Script is actually JScript with square bracket notation instead of dot notation. You can manipulate arrays in C#Script in the same way as in JScript (or JavaScript, which is similar):
// Define an array using an array literal
var names = ["Alice", "Bob", "Charlie"];
Log.Message(names[0]); // "Alice"
// Create and populate an array using a loop
var numbers = new Array(); // or: var numbers = [];
for (var i = 0; i < 5; i++) {
numbers[i] = i;
}
Log.Message(numbers.join()); // "0,1,2,3,4"