Arduino Uno ds18b20 and sure 2416 dor matrix display

if i change

itoa(temp,buffer,10);

to

ftoa(temp,buffer,10);

I receive this error

lcd24x16_base___temperatura.cpp: In function 'void loop()':
lcd24x16_base___temperatura:112: error: 'ftoa' was not declared in this scope

where is the problem ?