Implicit declaration of function and conflicting type - AVR

Question

This is my first program for AVR. While building, the code is showing error: conflicting types for 'Encode' implicit declaration of 'Encode'

I have written the following code:

#include <avr/io.h>
#include <util/delay.h>
#include <stdlib.h>

#define SegDataPort PORTC
#define SegDataPin PINC
#define SegDataDDR DDRC

#define SegCntrlPort PORTD
#define SegCntrlPin PIND
#define SegCntrlDDR DDRD

int main(void)
{
   SegDataDDR = 0xFF;
   SegCntrlDDR = 0xF3;
   SegCntrlPort = 0xF3;
   SegDataPort = 0x00;
   unsigned char adc_value;
   float volt = adc_value/1023;
   int temp = floor(volt*10 + 0.5);

   SegDataPort = Encode(temp1%10);

   //^^^^ implicit declaration of 'Encode' 

   SegCntrlPort = ~0x01;
   SegDataPort = Encode((temp1/10)%10);
   SegCntrlPort = ~0x02;
   SegDataPort = Encode(temp1/100);
   SegCntrlPort = ~0x04;
}

unsigned char Encode(int digit)
{
   unsigned char val;
   switch(digit)
   {
      case 0 : Val = 0b00111111;
      case 1 : val = 0b00000110;

      /// so on till case 9
   }
   return val;
}

I am using ATmega16 as microcontroller. I have also added much more libraries such as math for floor function and others. I have tried changing int to unsigned int, unsigned char and others but it is still not working and showing same error. Please help me.

Answer 1

implicit declaration of 'Encode'

In C a function needs to be either declared or defined before it has been used (called).

Either

• Move the definition of Encode() function before main()
• Add a forward declaration to Encode() before main().

That said, floor() is a function, defined in math.h and defined in the math library. To use that, you need to #include <math.h> and link with -lm at compilation time.

---

About the programmic logic used here,

unsigned char adc_value;
float volt = adc_value/1023;
int temp = floor(volt*10 + 0.5);

are pretty problematic, because

1. adc_value is used uninitialized, which leads to undefined behaviour.
2. adc_value is of type char. Dividing it by a value of 1023 will always give a result of 0 as the division will take place as an integer division and won't produce a float result itself, as you migh have expected.

My suggestions, change that code block to

int adc_value = <some value to initialize>;  //or some input function
float volt = (float)adc_value/1023;          //enforce floating point division
int temp = floor(volt*10 + 0.5);

Answer 2

First mistake:

 unsigned char adc_value;
 float volt = adc_value/1023;

You defind adc_value as an unsigned char and in the next line you tried to divide it by 1023 and assigned the result to a float type variable. You can't do these in C language. (More over you didn't assign any value to adc_value! it will be zero or a random value)

Second mistake:

Your second problem is that you defined your Encode function after calling it in main(). You must move the whole function before main() function or just add its prototype before the main() function.

i.e add unsigned char Encode(int digit); before main()

Thirst mistake:

You tried to assign some values to those variables that you declared with #define:

#define SegDataPort PORTC
#define SegDataPin PINC
#define SegDataDDR DDRC

#define SegCntrlPort PORTD
#define SegCntrlPin PIND
#define SegCntrlDDR DDRD

int main(void)
{
   SegDataDDR = 0xFF;
   SegCntrlDDR = 0xF3;
   SegCntrlPort = 0xF3;
   SegDataPort = 0x00;
   .
   .
   .

This is illegal also. those variables that is defined with #define, are constant and you must not try to change them in the program body.