## Chapter 2 – Decisions ### Making decisions All the programs we have seen so far have been predictable; they went straight through the instructions, then went back to the beginning again. This is not very useful. In practice the computer would be expected to make decisions and act accordingly. There are three ways *NextBASIC* helps you make decisions: The first is by using the **IF** keyword in a short, medium and long format, the second by using the **ON** *case selection* keyword and the third is by using the *select operator* **?** (question mark). ### Using IF… to make decisions The short and medium form of **IF** are as follows: **IF** *condition* **THEN** *action* [**ELSE** *alternative action*] Clear the previous program from memory by using **NEW** and type in and run the following example: ``` 10 REM Guess the number 20 INPUT "Enter the number to guess", a: CLS 30 INPUT "Guess the number", b 40 IF b=a THEN PRINT "That is correct": STOP 50 IF ba THEN PRINT "That is too big, try again" 70 GO TO 30 ``` You can see that in its simplest form an **IF** statement is: **IF** *condition* **THEN** *action* where *action* stands for a sequence of commands, separated by colons in the usual way. The condition is something that is going to be worked out as either true or false; if it comes out as true then the statements in the rest of the line after **THEN** are executed, but otherwise they are skipped over, and the program executes the next instruction. The simplest conditions compare two numbers or two strings: they can test whether two numbers are equal or whether one is bigger than the other; and they can test whether two strings are equal, or (roughly) one comes before the other in alphabetical order. They use the relations =, <, >, <=, >= and <>. Additionally we can use **NOT**, **AND**, **OR**, ! (bitwise NOT), **|** (bitwise OR), **&** (bitwise AND), ^**|** (bitwise XOR) all of which produce a *true* (**1**) or *false* (**0**) result = means *equals*. Although it is the same symbol as the = in a **LET** command, it is used in quite a different sense. < means *is less than* so that: **1 < 2**\ **-2 <-1**\ **-3 < 1** are all *true*, but: