Declare counter variable in for statements

Declaring the counter variable outside the for statement is done very rarely in actual programming, and only when there is a use for that variable outside the scope of the for loop (which is not the case here). I don't see any value in declaring the variable outside the statement in the example code, as it only teaches bad programming. In some cases, the example code snippets didn't even contain a declaration and so would not compile if copied into a sketch.

Author: per1234

Language/Structure/Control Structure/break.adoc

@@ -36,7 +36,7 @@ In the following code, the control exits the `for` loop when the sensor value ex
 [source,arduino]
 ----
 int threshold = 40;
-for (x = 0; x < 255; x ++) {
+for (int x = 0; x < 255; x ++) {
   analogWrite(PWMpin, x);
   sens = analogRead(sensorPin);
   if (sens > threshold) {     // bail out on sensor detect

Language/Structure/Control Structure/continue.adoc

@@ -36,7 +36,7 @@ The `continue` statement skips the rest of the current iteration of a loop (link
 The following code writes the value of 0 to 255 to the `PWMpin`, but skips the values in the range of 41 to 119.
 [source,arduino]
 ----
-for (x = 0; x <= 255; x ++) {
+for (int x = 0; x <= 255; x ++) {
   if (x > 40 && x < 120) {  // create jump in values
     continue;
   }

Language/Variables/Data Types/array.adoc

@@ -67,8 +67,7 @@ Arrays are often manipulated inside for loops, where the loop counter is used as
 
 [source,arduino]
 ----
-int i;
-for (i = 0; i < 5; i = i + 1) {
+for (byte i = 0; i < 5; i = i + 1) {
   Serial.println(myPins[i]);
 }
 ----

Language/Variables/Utilities/PROGMEM.adoc

@@ -71,7 +71,6 @@ const PROGMEM  uint16_t charSet[]  = { 65000, 32796, 16843, 10, 11234};
 const char signMessage[] PROGMEM  = {"I AM PREDATOR,  UNSEEN COMBATANT. CREATED BY THE UNITED STATES DEPART"};
 
 unsigned int displayInt;
-int k;  // counter variable
 char myChar;
 
 
@@ -81,14 +80,14 @@ void setup() {
 
   // put your setup code here, to run once:
   // read back a 2-byte int
-  for (k = 0; k < 5; k++) {
+  for (byte k = 0; k < 5; k++) {
     displayInt = pgm_read_word_near(charSet + k);
     Serial.println(displayInt);
   }
   Serial.println();
 
   // read back a char
-  for (k = 0; k < strlen_P(signMessage); k++) {
+  for (byte k = 0; k < strlen_P(signMessage); k++) {
     myChar =  pgm_read_byte_near(signMessage + k);
     Serial.print(myChar);
   }

Language/Variables/Utilities/sizeof.adoc

@@ -46,14 +46,13 @@ This program prints out a text string one character at a time. Try changing the
 [source,arduino]
 ----
 char myStr[] = "this is a test";
-int i;
 
 void setup() {
   Serial.begin(9600);
 }
 
 void loop() {
-  for (i = 0; i < sizeof(myStr) - 1; i++) {
+  for (byte i = 0; i < sizeof(myStr) - 1; i++) {
     Serial.print(i, DEC);
     Serial.print(" = ");
     Serial.write(myStr[i]);
@@ -73,7 +72,7 @@ Note that `sizeof` returns the total number of bytes. So for arrays of larger va
 int myValues[] = {123, 456, 789};
 
 // this for loop works correctly with an array of any type or size
-for (i = 0; i < (sizeof(myValues) / sizeof(myValues[0])); i++) {
+for (byte i = 0; i < (sizeof(myValues) / sizeof(myValues[0])); i++) {
   // do something with myValues[i]
 }
 ----