How to get close/open data?

Hi, wondered if anyone here knows how I should get the highest close/open and the lowest close/open price for the previous day?

It might be ok if I could just get the highest open and lowest close, but sometimes the lowest open can be lower than the close if that makes sense.

you can use iHighest and iLowest and set the mode to MODE_OPEN and MODE_CLOSE as needed. Here is the instructions for the iHighest command, the iLowest is the same:

int iHighest(string symbol, int timeframe, int type, int count=WHOLE_ARRAY, int start=0)Returns the shift of the maximum value over a specific number of periods depending on type.
Parameters:
symbol - Symbol the data of which should be used to calculate indicator. NULL means the current symbol.timeframe - Timeframe. It can be any of Timeframe enumeration values. 0 means the current chart timeframe.type - Series array identifier. It can be any of the Series array identifier enumeration values.count - Number of periods (in direction from the start bar to the back one) on which the calculation is carried out.start - Shift showing the bar, relative to the current bar, that the data should be taken from.
Sample:
double val; // calculating the highest value on the 20 consequtive bars in the range // from the 4th to the 23rd index inclusive on the current chart val=High[iHighest(NULL,0,MODE_HIGH,20,4)];