IFD:GrundlagenElektronik2011/BasicsCourse: Difference between revisions

IFD:GrundlagenElektronik2011/BasicsCourse (view source)

Revision as of 14:03, 19 January 2012

1,382 bytes added , 19 January 2012

no edit summary

Mschied

703

edits

@@ Line 143: / Line 143: @@
 now myNumber has the same value as anotherNumber and its value is printed.
+==== Testing roll over ====
+<source lang="c">
+void loop () {
+  Serial.println(myNumber);
+  myNumber = myNumber + 1;
+}
+</source>
+Each time the loop is started again the number is first sent to the computer and then increased by 1.
+Let the program run for a while and see what happens when the border of an integer variable is reached. (when reaching 32,767) the number is suddenly "wrapped over" to the most negative number possible: -32,768 and from there starts again countin towards 0 - reaching the limit at the upper and again and so on. This roll over can be used in programs to infinitely count - however since it is not obviously at what point the number will roll over it's no nice programming style.
+Now you can use the same program but use "unsiged int" instead int. Observe that now the number rolls over to 0 and not to a negative number.
+You can't only modify variables inside the loop function, but also in the setup fuction:
+<source lang="c">
+unsigned int myNumber;
+void setup () {
+  Serial.begin(9600);
+  Serial.println(myNumber);
+  myNumber = myNumber - 1;
+  Serial.println(myNumber);
+}
+void loop () {
+}
+</source>
+Now everything happens in the setup function - so it happens only once. Then the program will continue in the loop but there it does nothing and nothing and nothing again infinitely.
+Notice the roll over also happens in both directions.