# 'i' not declared in this scope **URL:** \ **Category:** Programming\ **Created:** [April 17, 2018, 9:37pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943 "2018-04-17T21:37:41Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![jonman5](https://avatars.discourse-cdn.com/v4/letter/j/c4cdca/32.png) [@jonman5](https://forum.arduino.cc/u/jonman5)\ **Post date:** [April 17, 2018, 9:37pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/1 "2018-04-17T21:37:41Z")
I don't understand I am getting the error message "'i' is not declared in this scope" even though it should be. It is originating from the line `if ((i)==1){` Here is my code: ```cpp #include //setting pin numbers AF_DCMotor motor1(1); AF_DCMotor motor2(2); AF_DCMotor motor3(3); AF_DCMotor motor4(4); const int trigpin = 53; const int echopin = 51; //setting up other variables int range; long duration; int distance; int start_turn=-15001; //defining threshold distance in cm const int t_d=20; void setup() {   Serial.begin(9600);          // set up Serial library at 9600 bps     //set up sensor input, output   pinMode(trigpin, OUTPUT);   pinMode(echopin, INPUT);   Serial.println("Start");     // turn on motors and set the speed of motors   motor1.setSpeed(255);   motor2.setSpeed(255);   motor3.setSpeed(255);   motor4.setSpeed(255);   motor1.run(RELEASE);   motor2.run(RELEASE);   motor3.run(RELEASE);   motor4.run(RELEASE);   } //defining the function for getting the range to nearest obstacle in cm int get_range() {   digitalWrite(trigpin, LOW);   delayMicroseconds(2);     digitalWrite(trigpin, HIGH);   delayMicroseconds(5);   digitalWrite(trigpin, LOW);   duration = pulseIn(echopin, HIGH);   distance = duration*0.034/2;   return distance; } void loop() {   range=get_range();   while ((range)>=(t_d)){     //Serial.print("forward");     motor1.run(FORWARD);     motor2.run(FORWARD);     motor3.run(FORWARD);     motor4.run(FORWARD);     range=get_range();   }   Serial.println(range);   while ((range)<(t_d)){     if (abs((millis()-(start_turn)))>10000){       randomSeed(analogRead(9));       const int i = (random(1, 256))%2;     }     if ((i)==1){       Serial.print("right");       motor1.run(BACKWARD);       motor2.run(BACKWARD);       motor3.run(FORWARD);       motor4.run(FORWARD);       range=get_range();       start_turn=millis();     }     else{       motor1.run(FORWARD);       motor2.run(FORWARD);       motor3.run(BACKWARD);       motor4.run(BACKWARD);       range=get_range();       start_turn=millis();     }     if (range>t_d){       delay(3000);     }       } } ``` ---
**Author:** ![pert](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/pert/32/217111_2.png) [@pert](https://forum.arduino.cc/u/pert)\ **Post date:** [April 17, 2018, 9:42pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/2 "2018-04-17T21:42:16Z")
Do some research on variable scope: [https://www.arduino.cc/reference/en/language/variables/variable-scope--qualifiers/scope/](https://www.arduino.cc/reference/en/language/variables/variable-scope--qualifiers/scope/) You've declared i within this scope: ```cpp     if (abs((millis()-(start_turn)))>10000){       randomSeed(analogRead(9));       const int i = (random(1, 256))%2;     } ``` so you can only use it within that scope. ---
**Author:** ![CrossRoads](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/crossroads/32/214033_2.png) [@CrossRoads](https://forum.arduino.cc/u/CrossRoads)\ **Post date:** [April 17, 2018, 9:42pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/3 "2018-04-17T21:42:45Z")
add byte i; before setup() so it's a global variable. ---
**Author:** ![UKHeliBob](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/ukhelibob/32/215663_2.png) [@UKHeliBob](https://forum.arduino.cc/u/UKHeliBob)\ **Post date:** [April 17, 2018, 9:44pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/4 "2018-04-17T21:44:39Z")
> CrossRoads: > add > byte i; > before setup() > so it's a global variable. and don't put const int in front of it when you assign the random number to it otherwise you will have 2 different variables with the same name but different scopes ---
**Author:** ![jonman5](https://avatars.discourse-cdn.com/v4/letter/j/c4cdca/32.png) [@jonman5](https://forum.arduino.cc/u/jonman5)\ **Post date:** [April 17, 2018, 10:02pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/5 "2018-04-17T22:02:19Z")
Thanks guys, I'm not very experienced with coding for Arduino or in C++ in general so I didn't understand the scope thing totally because it is different from other languages I've learned so far. I'm going to use what you guys suggested. ---
**Author:** ![arduino\_new](https://avatars.discourse-cdn.com/v4/letter/a/dc4da7/32.png) [@arduino\_new](https://forum.arduino.cc/u/arduino_new)\ **Post date:** [April 17, 2018, 11:14pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/6 "2018-04-17T23:14:30Z")
> jonman5: > Thanks guys, I'm not very experienced with coding for Arduino or in C++ in general so I didn't understand the scope thing totally because it is different from other languages I've learned so far. > > I'm going to use what you guys suggested. General rule is everything declared inside {} will only live in that {}. If you want to pursue further, I suggest to learn more about scoping and not giving up by using global variables when it's not necessary because it's a potentially hazard. ---
**Author:** ![system](https://dub1.discourse-cdn.com/arduino/user_avatar/forum.arduino.cc/system/32/1140315_2.png) [@system](https://forum.arduino.cc/u/system)\ **Post date:** [May 5, 2021, 11:08pm UTC](https://forum.arduino.cc/t/i-not-declared-in-this-scope/520943/7 "2021-05-05T23:08:21Z")
Closed on May 5, 2021, 11:08pm UTC