AP Computer Science A

## Algorithms and sequencing An **algorithm** is a step-by-step process for completing a task or solving a problem. Everyday processes are algorithms: a recipe, directions to a friend's house, the steps for making a phone call. An algorithm can be written in ordinary language or drawn as a diagram such as a flowchart, and writing one out before any code is a good habit because it shows which steps the program needs and in what order. **Sequencing** is the ordering of the steps. The steps of a process are carried out one at a time, and the order matters, because changing it can change the result. Consider this algorithm for making a sandwich with cheese and butter: 1. Take two slices of bread. 2. Spread butter on one slice. 3. Place cheese on the buttered slice. 4. Place the second slice on top. If step 4 came before step 3 the cheese would have nowhere to go. A program is an algorithm written in a language a computer can follow, and a Java program runs its statements in order from top to bottom unless a statement changes the flow of control. ```java int width = 4; int height = 3; int area = width * height; System.out.println(area); ``` This prints 12. Swapping the third and fourth lines would not compile or would print the wrong thing, because `area` would be used before it has a value. ## Writing, compiling and running Java Java source code is plain text and can be written in any text editor. Most programmers use an **integrated development environment** (IDE), which…