Here is the code:

const int trig = 9;
const int echo = 10;
const int redswitch = 2;
const int yellowswitch = 3;
int redled = 6;
int greenled = 5;
volatile int pwm = 50;

volatile bool rs = HIGH;      //RS - RED SWITCH
volatile bool ys = HIGH;      //YS - YELLOWSWITCH

volatile long distance=0;
long duration=0;
long temp=0;

void setup(){
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(redled,OUTPUT);
  pinMode(greenled,OUTPUT);
  pinMode(redswitch,INPUT);
  pinMode(yellowswitch,INPUT);
  Serial.begin(9600);
  
  attachInterrupt(digitalPinToInterrupt(redswitch), red,CHANGE);
  attachInterrupt(digitalPinToInterrupt(yellowswitch), green,CHANGE);
    
  constrain(pwm,0,255);
  
  digitalWrite(greenled,LOW);
  digitalWrite(redled,LOW);
}

void loop(){

  
  //Ultrasonic sensor's distance calculation
  digitalWrite(trig,LOW);
  delayMicroseconds(5);

  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  distance = temp;
  duration = pulseIn(echo,HIGH);
  distance = duration * 0.0343 /2;

  Serial.println(distance);  
  analogWrite(redled,pwm);
  analogWrite(greenled,pwm);
}

void red(){
  rs = digitalRead(redswitch);
  if(distance>8 && rs == HIGH) pwm = 150;
  else pwm = 0;
  analogWrite(redled,pwm);
  
}

void green(){
  ys = digitalRead(yellowswitch);
  if(distance>8 && ys == HIGH) pwm = 250;
  else pwm = 0;
  
}

Here is the code:(updated)

const int trig = 9;
const int echo = 10;
const int redswitch = 2;
const int yellowswitch = 3;
int redled = 6;
int greenled = 5;
volatile int pwm = 50;

volatile bool rs = LOW;      //RS - RED SWITCH
volatile bool ys = LOW;      //YS - YELLOWSWITCH
bool last_rs = LOW;
bool last_ys =  LOW;
volatile long distance=0;
long duration=0;
long temp=0;

void setup(){
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(redled,OUTPUT);
  pinMode(greenled,OUTPUT);
  pinMode(redswitch,INPUT);
  pinMode(yellowswitch,INPUT);
  Serial.begin(9600);
 
  attachInterrupt(digitalPinToInterrupt(redswitch), red,CHANGE);
  attachInterrupt(digitalPinToInterrupt(yellowswitch), green,CHANGE);
      
  digitalWrite(greenled,LOW);
  digitalWrite(redled,LOW);
}

boolean debounce(boolean temp,int switchPin)
{
  boolean current = digitalRead(switchPin);
  if (temp != current)
  {
    delay(5);
    current = digitalRead(switchPin);
  }
  return current;
}

void loop(){

  
  //Ultrasonic sensor's distance calculation
  digitalWrite(trig,LOW);
  delayMicroseconds(5);

  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  
  duration = pulseIn(echo, HIGH);
  temp = duration * 0.0343 / 2;
  noInterrupts();
  distance = temp;
  rs = debounce(last_rs,redswitch);
  ys = debounce(last_ys,yellowswitch);
  last_rs = rs;
  last_ys = ys;
  if(distance>8)interrupts();
  
  Serial.println(distance);  
  analogWrite(redled,pwm);
  analogWrite(greenled,pwm);
}

void red(){
  
  if(rs == HIGH) pwm = 150;
  else pwm = 0;
  
  
}

void green(){
  
  if(ys == HIGH) pwm = 250;
  else pwm = 0;
  
}

Alright. This is the task:

Make a circuit and code your arduino such that there are 2 tactile switches, each with a predefined pwm value. Whenever any one button is pressed the led should run at that pwm value, until the button is released. There is also an ultrasonic sensor on the same arduino that triggers an interrupt at a threshold distance that stops the led. When no button is pressed or the ultrasonic isnt active, the led should run at another pwm value.

Here is the code:

const int trig = 9;
const int echo = 10;
const int redswitch = 2;
const int yellowswitch = 3;
int redled = 6;
int greenled = 5;
volatile int pwm = 50;

volatile bool rs = HIGH;      //RS - RED SWITCH
volatile bool ys = HIGH;      //YS - YELLOWSWITCH

volatile long distance=0;
long duration=0;
long temp=0;

void setup(){
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(redled,OUTPUT);
  pinMode(greenled,OUTPUT);
  pinMode(redswitch,INPUT);
  pinMode(yellowswitch,INPUT);
  Serial.begin(9600);
  
  attachInterrupt(digitalPinToInterrupt(redswitch), red,CHANGE);
  attachInterrupt(digitalPinToInterrupt(yellowswitch), green,CHANGE);
    
  constrain(pwm,0,255);
  
  digitalWrite(greenled,LOW);
  digitalWrite(redled,LOW);
}

void loop(){

  
  //Ultrasonic sensor's distance calculation
  digitalWrite(trig,LOW);
  delayMicroseconds(5);

  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  distance = temp;
  duration = pulseIn(echo,HIGH);
  distance = duration * 0.0343 /2;

  Serial.println(distance);  
  analogWrite(redled,pwm);
  analogWrite(greenled,pwm);
}

void red(){
  rs = digitalRead(redswitch);
  if(distance>8 && rs == HIGH) pwm = 150;
  else pwm = 0;
  analogWrite(redled,pwm);
  
}

void green(){
  ys = digitalRead(yellowswitch);
  if(distance>8 && ys == HIGH) pwm = 250;
  else pwm = 0;
  
}

Now, when the arduino is connected to my laptop, led runs at the a particular value. But whenever I press a button they go off. Can you help me find out what's wrong here?

Alright. This is what I wanted to do:

Make a circuit and code the arduino such that there are 2 tactile switches, each with a predefined pwm value. Whenever any one button is pressed the led should run at that pwm value, until the button is released. There is also an ultrasonic sensor on the same arduino that triggers an interrupt at a threshold distance that stops the led. When no button is pressed or the ultrasonic isnt active, the led should run at another pwm value.

Here is the code:

const int trig = 9;
const int echo = 10;
const int redswitch = 2;
const int yellowswitch = 3;
int redled = 6;
int greenled = 5;
volatile int pwm = 50;

volatile bool rs = HIGH;      //RS - RED SWITCH
volatile bool ys = HIGH;      //YS - YELLOWSWITCH

volatile long distance=0;
long duration=0;
long temp=0;

void setup(){
  pinMode(trig,OUTPUT);
  pinMode(echo,INPUT);
  pinMode(redled,OUTPUT);
  pinMode(greenled,OUTPUT);
  pinMode(redswitch,INPUT);
  pinMode(yellowswitch,INPUT);
  Serial.begin(9600);
  
  attachInterrupt(digitalPinToInterrupt(redswitch), red,CHANGE);
  attachInterrupt(digitalPinToInterrupt(yellowswitch), green,CHANGE);
    
  constrain(pwm,0,255);
  
  digitalWrite(greenled,LOW);
  digitalWrite(redled,LOW);
}

void loop(){

  
  //Ultrasonic sensor's distance calculation
  digitalWrite(trig,LOW);
  delayMicroseconds(5);

  digitalWrite(trig,HIGH);
  delayMicroseconds(10);
  digitalWrite(trig,LOW);
  distance = temp;
  duration = pulseIn(echo,HIGH);
  distance = duration * 0.0343 /2;

  Serial.println(distance);  
  analogWrite(redled,pwm);
  analogWrite(greenled,pwm);
}

void red(){
  rs = digitalRead(redswitch);
  if(distance>8 && rs == HIGH) pwm = 150;
  else pwm = 0;
  analogWrite(redled,pwm);
  
}

void green(){
  ys = digitalRead(yellowswitch);
  if(distance>8 && ys == HIGH) pwm = 250;
  else pwm = 0;
  
}

Now, when the arduino is connected to my laptop, led runs at the a particular value. But whenever I press a button they go off. Can you help me find out what's wrong here?