Capacitive Touch Lamp - Mode Problems

Using Arduino Programming Questions
2 
    if (mode = 0) analogWrite(LEDPin, 0);
    if (mode = 1) analogWrite(LEDPin, 100);
    if (mode = 2) analogWrite(LEDPin, 150);
    if (mode = 3) analogWrite(LEDPin, 254);
    if (mode == 4) mode = 0;

Spot the difference between these lines ?
Only one of them tests the value of mode.