Diff: main.cpp

Revision:

109:744c6cb711bf

Parent:

108:eee3167b25b4

Child:

110:8170476d91a6

--- a/main.cpp	Tue Sep 21 02:00:55 2021 +0000
+++ b/main.cpp	Thu Sep 23 03:03:59 2021 +0000
@@ -1,31 +1,67 @@
 /*
-    Project: BinaryCount
+    Project: Button Tests
     File: main.cpp
     
-    Displays 8 bit binary count on bar graph display.
+    This program demonstrates User Button behavior.
     
     Written by: Dr. C. S. Tritt
-    Created: 9/20/21 (v. 1.2)
+    Created: 9/22/21 (v. 1.0)
 */
 #include "mbed.h"
 
-BusOut barGraph(D2, D3, D4, D5, D6, D7, D8, D9);  // Create BusOut object.
+DigitalIn uB(USER_BUTTON); // Active low! Normally 1 go to 0 when pressed.
 
 int main() {
-    // Test the wiring.
-    barGraph = 0;  // All bars off (base 10).
-    ThisThread::sleep_for(400); // For 0.4 seconds.
-    barGraph = 0b01010101;  // Odd bars on (binary).
-    ThisThread::sleep_for(400); // Test even bars for 0.4 seconds. 
-    barGraph = 0b10101010;  // Even bars on (binary).   
-    ThisThread::sleep_for(400); // Test even bars for 0.4 seconds.
-    barGraph = 0xFF;  // All bars on. Hex.
-    ThisThread::sleep_for(400); // For 0.4 seconds.
-    // Enter main loop.   
+    // Enter main loop. Sequential calls to the button like this is generally
+    // not good practice, but I want to use the DigitalIn object in these 
+    // contexts to illustrate my points. See while loop below for a better 
+    // (more common and realistic) approach.   
     while(true) {
-        for (int i = 0; i < 256; i++) { // Add one to count.
-            barGraph = i;  // Copy the count to the bargraph.
-            ThisThread::sleep_for(100);  // Display the value for 0.1 seconds.
-        }
-    }
-}
\ No newline at end of file
+        // Use the button in some printf calls.
+        printf("\nuB (w/o cast) = %d.\n", uB); // Bad! Warning! Wrong!
+        printf("uB (with int cast) = %d.\n", static_cast<int>(uB));
+        // I found a reference that claimed there is a %b (or B) speicifer for 
+        // type bool, but it doesn't work in mbed.  
+        printf("uB (with bool cast) = %d.\n", static_cast<bool>(uB));                              
+        printf("uB.read = %d.\n", uB.read());  
+        
+        // Use the button in some if constructs. No need to compare. No need to
+        // use .read().   
+        if (uB) 
+            printf("In if (uB).\n");
+        if (uB.read()) 
+            printf("In if (uB.read()).\n");
+        if (!uB) 
+            printf("In if (!uB).\n");
+        if (!uB.read()) 
+            printf("In if (!uB.read()).\n");
+        ThisThread::sleep_for(500); // For 0.5 seconds after some output.
+    
+        // Best practice is to get and save the button state and use until you  
+        // are done with your response to it.
+        int count = 5; // Count for loop below.
+        bool uBstate = uB; // Get the buttons state. Save it and use it.
+        // uB could change states between the if below and the following while. 
+        // This would result in an extra line of output without the contents of 
+        // the while being output. That is what the use of uBstate prevents.
+        if (!uBstate) printf("\n"); // Print extra line before while output.
+        while (!uBstate && count >= 1) {
+            // Count down from 5 to 1.
+            // Do something here with uBstate false & assuming uB is false.
+            // Decrement after use!
+            printf("In while loop. Count = % d.\n", count--);
+            // Now determine if state has changed.
+            if (uB != uBstate) {
+                printf("The button changed while in the loop. Exiting.\n");
+                // Using a while and setting exit conditions is generally better 
+                // than using a break. Strive for one way in and one way out in
+                // all your code for more reliability and easier maintenance. 
+                // But there are exceptions to this rule. That is why break (and 
+                // continue exist. 
+                uBstate = !uBstate; // Update uBstate to exit loop.
+            } //end of if.
+        ThisThread::sleep_for(500); // For 0.5 seconds in while.
+        } // end of !uBstate while.
+        printf("End of main while.\n\n");
+    } // end of main while.
+} // end of main function.
\ No newline at end of file