DECISIONS, DECISIONS in Font

Encoding Data Matrix 2d barcode in Font DECISIONS, DECISIONS

Figure 12-13. Three possible paths for the SWITCH block Notice that there is now a new row in the Condition section: 1. 2. 3. 0 1 2

There are now three tabs on the SWITCH block. Tab 3 will have its blocks executed if the SWITCH block detects a Number value of 2. Here you have a small problem: SPOT will pick only 1, 2, or 3. But the only options shown are 0, 1, and 2. How can you change this If you click one of the conditions, you can change its value in the text box just below the Condition section. First, click the condition whose value you want to change (see Figure 12-14).

Figure 12-14. Click a Condition to change its value. In this example, the third condition is selected, which has a default value of 2. In the box below the conditions, enter the value of 3 as seen in Figure 12-15 and press Enter.

Figure 12-15. Select a condition you wish to change by clicking on it. You ll do this for the first and second conditions also, changing their respective values to 1 and 2, as seen in Figure 12-16.

Finally, you may have noticed the checkmark next to a condition. In Figure 12-16 it is next to the second condition (indicated by the numeral 2). The checkmark indicates which condition the SWITCH block considers the default value to use and the tab (and its blocks) to select if the SWITCH block is unable to make a decision. For example, suppose I had configured the RANDOM block to select a value between 1 and 5. There are no conditions specified for what to do if a 4 or 5 is randomly selected. Suppose you wish a 4 or 5 to be treated as a value of 3. In this case, the blocks found on the third tab will be executed because you have selected condition 3 by selecting the third condition and clicking on the small asterisk button (*), as seen in Figure 12-17.

Note When a SWITCH block is encountered, something must be done. One of the conditions must be satisfied

for the program to continue running. Therefore, a default condition must be specified in most instances. You can always leave a path empty, with no NXT-G blocks on it, for one of the conditions. In cases where you have a program that should not react to a condition, provide a blank path and set that blank path as the default. Then, if a sensor or RANDOM block or other block does not trigger a suitable condition you ve specified for the SWITCH block, the default condition will be chosen and no blocks executed, allowing the SWITCH block to complete and the program to continue.

Caution Please be aware that you cannot have two or more conditions with the same Number value. This is

because the SWITCH block would get confused and not know which path to take. Make sense If condition 1 has a Number value of 1 and condition 2 has a Number value of 1, which path would the SWITCH block take if the RANDOM block sends a value of 1 Fortunately, the SWITCH block is smart and will not allow you to make this mistake.

Execution!

Now that you ve configured the three conditions and the default (condition 3), you can drop in a collection of MOVE blocks that will allow SPOT to turn left, turn right, or move forward. If SPOT picks 1, then he turns left. So, you ll click the first tab (see Figure 12-18) and drop in a MOVE block that will allow SPOT to turn left.