AVR Freaks

I wrote this program, but compiling it gives the following warning: Implicit declaration of function dtostrf. If I ignore the warning, the display always shows zero after decimal, even if I put an arbitrary value. 

For example, when it should be showing 15.2, it shows 15.0.

Please advise. Thank you!

#include <avr/io.h>             // special function registers
#include <stdio.h>              // sprintf()
#define F_CPU 4000000           // 4MHz RC
#include <util/delay.h>         // _delay_xx()
#include "lcd.h"                // Fleury LCD library


int readADC(char channel)


{
	ADMUX = (3 << REFS0)|(1<<ADLAR)|(channel << MUX0);    // VREF=2.56V, 8-bit, PA0. PA1
	_delay_us(10);              // allow multiplexer to settle
	ADCSRA |= (1<<ADSC);        // Start Conversion
	while (ADCSRA & (1<<ADSC)); // wait for completion
	return ADCH;                // 8-bit result because we use ADLAR

}

int main(void)

{
	char channel, din[16], dout[16], finalTIN[5], finalTOUT[5], degree = 0xDF; 
	int k, m, ind = 0, oud = 0, find = 0, foud = 0;
	float tempIN, tempOUT; 
	ADCSRA = (1<<ADEN)|(7 << ADPS0);        //div128

	lcd_init(LCD_DISP_ON);
	

		
		lcd_clrscr();
		lcd_puts("READING...");
		

		
		
		while (1) {
			
		ind = 0, oud = 0, find = 0, foud = 0;
			
			for (k=1; k<11; k++)
			{
			channel = 0;
			ind = readADC(channel); 
			_delay_ms(500);
			find = find + ind;		
			}
			
			for (m=1; m<11; m++)
			{
			channel = 1;
			oud = readADC(channel);
			_delay_ms(500);
			foud = foud + oud;
			}
			
			lcd_clrscr();
			
			tempIN = find/10;
			dtostrf(tempIN, 4, 1, finalTIN);
			sprintf(din, "ROOM TEMP:%s%cC", finalTIN, degree);
			
			lcd_gotoxy(0,0);                                             
			lcd_puts(din);
			
		
			tempOUT = foud/10  //even if I write foud = 152, the output is 15.0 always.
			dtostrf(tempOUT, 4, 1, finalTOUT);		
			sprintf(dout,"AQUARIUM:%s%cC", finalTOUT, degree);    
			lcd_gotoxy(0,1);
			lcd_puts(dout);
		
		
			
	
		
	}
}