I have editted some codes. Kindly merge them.

blind_stick.ino

@@ -1,56 +1,55 @@
-/*
-* Ultrasonic Sensor HC-SR04 and Arduino Tutorial
-*
-* by Dejan Nedelkovski,
-* www.HowToMechatronics.com
-*
-*/
-// defines pins numbers
-const int trigPin = 9;
-const int echoPin = 10;
-int buzzer = 11;
-// defines variables
-long duration;
-int distance;
-void setup() {
-pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
-pinMode(echoPin, INPUT); // Sets the echoPin as an Input
-pinMode(buzzer, OUTPUT);
-Serial.begin(9600); // Starts the serial communication
-}
-void loop() {
-// Clears the trigPin
-digitalWrite(trigPin, LOW);
-delayMicroseconds(2);
-// Sets the trigPin on HIGH state for 10 micro seconds
-digitalWrite(trigPin, HIGH);
-delayMicroseconds(10);
-digitalWrite(trigPin, LOW);
-// Reads the echoPin, returns the sound wave travel time in microseconds
-duration = pulseIn(echoPin, HIGH);
-// Calculating the distance
-distance= duration*0.034/2;
-// Prints the distance on the Serial Monitor
-Serial.print("Distance: ");
-Serial.println(distance);
-if(distance <= 100){
-  tone(buzzer , 2000 , 500);
-}
-else if(distance <= 200){
-  tone(buzzer , 2000 , 500);
-  delay(500);
-}
-else if(distance <= 300){
-  tone(buzzer , 2000 , 500);
-  delay(1000);
-}
-else if(distance <= 400){
-  tone(buzzer , 2000 , 500);
-  delay(1500);
-}
-//else{
-//  digitalWrite(buzzer, LOW);
-//  delay(100);
-//}
-
+//Ultrasonic Sensor HC-SR04 and Arduino are the major components used
+
+// defines pins numbers
+const int trigPin = 9;
+const int echoPin = 10;
+int buzzer = 11;
+
+// defines variables
+long duration;
+int distance;
+
+void setup() {
+  pinMode(trigPin, OUTPUT); // Sets the trigPin as an Output
+  pinMode(echoPin, INPUT); // Sets the echoPin as an Input
+  pinMode(buzzer, OUTPUT);  //Sets the buzzer as an Output
+  Serial.begin(9600); // Starts the serial communication
+}
+void loop() {
+
+  // Clears the trigPin
+  digitalWrite(trigPin, LOW);
+  delayMicroseconds(2);
+
+  // Sets the trigPin on HIGH state for 10 micro seconds
+  digitalWrite(trigPin, HIGH);
+  delayMicroseconds(10);
+  digitalWrite(trigPin, LOW);
+
+  // Reads the echoPin, returns the sound wave travel time in microseconds
+  duration = pulseIn(echoPin, HIGH);
+
+  // Calculating the distance
+  distance= duration*0.034/2;
+
+  // Prints the distance on the Serial Monitor
+  Serial.print("Distance: ");
+  Serial.println(distance);
+
+  //According to the distance measured by sensor , the frequency of beep sound is modified 
+  if(distance <= 100){
+    tone(buzzer , 2000 , 500);
+  }
+  else if(distance <= 200){
+    tone(buzzer , 2000 , 500);
+    delay(500);
+  }
+  else if(distance <= 300){
+    tone(buzzer , 2000 , 500);
+    delay(1000);
+  }
+  else if(distance <= 400){
+   tone(buzzer , 2000 , 500);
+   delay(1500);
+  }  
 }