stepper motor help me

My project light-sensitive automatic opening and closing curtains…stepper motor does not stop after 90 degrees

// This Arduino example demonstrates bidirectional operation of a 
// 28BYJ-48, using a ULN2003 interface board to drive the stepper.
// The 28BYJ-48 motor is a 4-phase, 8-beat motor, geared down by
// a factor of 68. One bipolar winding is on motor pins 1 & 3 and
// the other on motor pins 2 & 4. The step angle is 5.625/64 and the 
// operating Frequency is 100pps. Current draw is 92mA. 
////////////////////////////////////////////////

//declare variables for the motor pins
int motorPin1 = 2;    // Blue   - 28BYJ48 pin 1
int motorPin2 = 4;    // Pink   - 28BYJ48 pin 2
int motorPin3 = 3;    // Yellow - 28BYJ48 pin 3
int motorPin4 = 5;    // Orange - 28BYJ48 pin 4
 int sayi;
int sayii; // Red    - 28BYJ48 pin 5 (VCC)
int ldr = 0;            
int ldr_value = 10;
int motorSpeed = 1200;  //variable to set stepper speed
int count = 0;          // count of steps made
int countsperrev = 256; // number of steps per full revolution
int lookup[8] = {B01000, B01100, B00100, B00110, B00010, B00011, B00001, B01001};

//////////////////////////////////////////////////////////////////////////////
void setup() {
  //declare the motor pins as outputs
  pinMode(motorPin1, OUTPUT);
  pinMode(motorPin2, OUTPUT);
  pinMode(motorPin3, OUTPUT);
  pinMode(motorPin4, OUTPUT);
  Serial.begin(9600);
}

//////////////////////////////////////////////////////////////////////////////
void loop(){
  if(ldr_value = analogRead(ldr))
  {
     Serial.println(ldr_value);                 //prints the LDR values to serial monitor
  delay(10); 
    clockwise();
  }
  else if (count == countsperrev * 2)
  {
    count = 0;}
  else{
    anticlockwise();
  count++;
}
}

//////////////////////////////////////////////////////////////////////////////
//set pins to ULN2003 high in sequence from 1 to 4
//delay "motorSpeed" between each pin setting (to determine speed)
void anticlockwise()
{
  
  for(int i = 0; i < 8; i++)
  {
    setOutput(i);
    delayMicroseconds(motorSpeed);
  }
  
}

void clockwise()
{
  
  
  for(int i = 7; i >= 0; i--)
  {
    setOutput(i);
    delayMicroseconds(motorSpeed);
  }
  
}

void setOutput(int out)
{
  digitalWrite(motorPin1, bitRead(lookup[out], 0));
  digitalWrite(motorPin2, bitRead(lookup[out], 1));
  digitalWrite(motorPin3, bitRead(lookup[out], 2));
  digitalWrite(motorPin4, bitRead(lookup[out], 3));
}
 if(ldr_value = analogRead(ldr))
  {
     Serial.println(ldr_value);                 //prints the LDR values to serial monitor
  delay(10); 
    clockwise();
  }
  else if (count == countsperrev * 2)
  {
    count = 0;}
  else{
    anticlockwise();
  count++;
}

this condition statement is false make ensure your ldr_value assigned properly.

Need == here

if(ldr_value = analogRead(ldr))