Converting Dates

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If a date is input to a for in the style DD-MM-YY or DD/MM/YY how would i change that into a timestamp value to store in a mysql database?

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I really want is people to enter the date as DD-MM-YY or DD/MM/YY then it to be stored in the data base and displayed as DD-MM-YY but mysql stores dates as YYYY-MM-DD which will confuse people when they look at my site so i thought the best way would be to convert the date to a timestamp to store it and then convert it back to the date to display it. Aslo the input for is an array which makes it slightly harder to code i think

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Dont anyone understand what i want or want to help me??