Chapter 5. Decisions


  • To be able to implement decisions using if statements

  • To effectively group statements into blocks

  • To learn how to compare integers, floating-point numbers, strings, and objects

  • To correctly order decisions in multiple branches and nested branches

  • To program conditions using Boolean operators and variables

    T To be able to design tests that cover all parts of a program

The programs we have seen so far were able to do fast computations and render graphs, but they were very inflexible. Except for variations in the input, they worked the same way with every program run. One of the essential features of nontrivial computer programs is their ability to make decisions and to carry out different actions, depending on the nature of the inputs. The goal of this chapter is to learn how to program simple and complex decisions.

The if Statement

Computer programs often need to make decisions, taking different actions depending on a condition.

Consider the bank account class of Chapter 3. The withdraw method allows you to withdraw as much money from the account as you like. The balance just moves ever further into the negatives. That is not a realistic model for a bank account. Let's implement the withdraw method so that you cannot withdraw more money than you have in the account. That is, the withdraw method must make a decision: whether to allow the withdrawal or not.

The if statement is used to implement a decision. The if statement has two parts: a condition and a body. ...

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