If we want to calculate the distance from the array which contains the coordinates i.e Latitude and Longitude then use the following code-

-(void) getDistanceFromArray {
  CLLocationDistance totalKilometers = 0;
  for (int i = 0; i < (self.arrayName.count - 1); i++) // <-- count - 1
  {
     CLLocation *loc1 = [self cLLocationFromString:[self.arrayName objectAtIndex:i]];
     CLLocation *loc2 = [self cLLocationFromString:[self.arrayName objectAtIndex:(i + 1)]];

     CLLocationDistance distance = [loc1 distanceFromLocation:loc2];
     CLLocationDistance kilometers = distance / 1000.0;
     totalKilometers += kilometers;
  }
  self.distanceString = [NSString stringWithFormat:@"%f", totalKilometers];
}

Here distanceString is the property of NSString type which convert the total distance into NSString.

Latitude and Longitude should be comma seprated.

-(CLLocation*) cLLocationFromString:(NSString*)string
{
    NSArray *coordinates = [string componentsSeparatedByString:@","];
    CGFloat latitude  = [[coordinates objectAtIndex:0] doubleValue];
    CGFloat longitude = [[coordinates objectAtIndex:1] doubleValue];
    return [[CLLocation alloc]  initWithLatitude:latitude longitude:longitude];
}