So is your project configured to use Redlib, Newlib or NewlibNano as your selected C library?
What are Redlib and Newlib?
If you are using Redlib, then make sure you haven't got CR_INTEGER_PRINTF symbol defined:
Using printf()
And if you are using NewlibNano, then make sure you have "Enable printf/scanf float" enabled in Project properties:
Newlib-Nano Support
If you need further assistance, then please confirm the version of LPCXpresso IDE that you are using, and export and post an example project that shows up your problem:
https://community.nxp.com/message/630625
Regards,
LPCXpresso Support