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cs31s11dis5 - CS31 Introduction to Computer Science I...

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Discussion 1H Notes (Week 5, April 29) TA: Brian Choi ([email protected]) Section Webpage: http://www.cs.ucla.edu/~schoi/cs31 Arrays Suppose you want to create 10 integer variables. Using what we know, we can do the following: int x1, x2, x3, x4, ... , x10; That is long, but still doable. What if, though, we want to make 100 of them, or 1000 of them? C++ provides a simple way of creating variables of the same type in a single statement. This is how: int a[100]; // declaration This will create an array of integers of length 100, where each item in the array can be referred to as: a[i] where i is the index ranging from 0 to 99, or 0 to length-1. (Does this sound familiar?) a[i] is an integer variable, and happens to be in the location i of the array a . When you declare an array, you must specify the size of the array you’re declaring, and the size must be a positive integer constant . A constant is either a value itself (e.g., 5, 10, 100) or a variable that is explicitly declared to be a constant (e.g., const int N = 10; ), such that the value of it can’t be changed. An example helps you understand how this works. What does the following program do? You can treat each element of the array as if it were a variable (since it IS a variable). You can therefore do: x[3] = 5; x[1]++; cout << x[i] << endl; CS31: Introduction to Computer Science I Spring 2011 Copyright Brian Choi 2011. All Rights Reserved. Week 5, Page 1/4 int sum(int m, int n); // sum from numbers m to n int main() { int sums[100]; // This is our array, creating 100 adjacent variables.
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