relay on off on the basis of others relay operation condition

i want on/off 1 relay on basis of other relay operation condition.
i trued in way.but if loop doesn't work.please me

#define relay2  46
#define relay4  30
#define relay3  31
  pinmode(relay2, output);
  pinmode(relay3, output);
  pinmode(relay4, output);

  if(relay3==low)
  {
 digitalwrite(relay4,low);
 if(current01>0.50)
 {
   digitalwrite(relay3,high);
 }
  }

try:

code: [select]

#define relay2  46
#define relay4  30
#define relay3  31
void setup()
{
  pinmode(relay2, output);
  pinmode(relay3, output);
  pinmode(relay4, output);
}
void loop()
{
  if (digitalread(relay3) == low)
  {
    digitalwrite(relay4, low);
    if (current01 > 0.50)
    {
      digitalwrite(relay3, high);
    }
  }
} 

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