Calculating intensity for an RGB Color

i would like to ask how i can calculate my variable y for an RGB color intensity.

These r,g,b letters in my RGB_Trypel struct are representing each array element for the arrays rot, gelb, gruen, weiss, schwarz. So i need here to multiply these r,g,b array elements with the shown numbers in my y variable.

i would really be glad for some help.

#define CRT_SECURE_NO_WARNINGS
#include <stdio.h>

struct RGB_Trypel
	{
		
	unsigned char r, g, b; // speichert Werte nur bis 255 und positive Werte

	};




int main(void)
{
	
	struct RGB_Trypel rot = { 255,0,0 }, gelb = { 255,255,0 }, gruen = { 0,255,0 };

	const  struct RGB_Trypel weiss = { 255,255,255 };
	const  struct RGB_Trypel schwarz = { 0,0,0 };

	struct RGB_Trypel fafeld[5] = { rot, gelb, gruen, weiss, schwarz };
	int n = 5;
	
	unsigned char intensiteat(struct RGB_Trypel t);
	{
		int = y;
		

		y = 0.299 * r + 0.587 * g + 0.114 * b;
	}
	


	for (int i = 0; i < n; i++)
	{

		printf("(%3d,%3d,%3d): \t intensiteat(%d) \n",fafeld[i].r, fafeld[i].g, fafeld[i].b, intensiteat(fafeld[i]);


	}


	return 0;
}

I am not really sure how i can put my struct array element into a function and let it multiply following numbers in my y variable.

Your big problem here is that this

 unsigned char intensiteat(struct RGB_Trypel t);
{
    int = y;
    

    y = 0.299 * r + 0.587 * g + 0.114 * b;
}

looks like an attempt to define a function inside another function. This wont work. Move it to be before main. Like this:

 unsigned char intensiteat(struct RGB_Trypel t)
{
    int = y;
    

    y = 0.299 * r + 0.587 * g + 0.114 * b;
}


 int main(void)
 {

second, to refer to fields of a struct inside that function do this:

 unsigned char intensiteat(struct RGB_Trypel t)
{
    int = y;
    

    y = 0.299 * t.r + 0.587 * t.g + 0.114 * t.bb;
}

you have multiple other errors, but this will get you started

BTW you missed an _ of the front the that define. Should be:

#define _CRT_SECURE_NO_WARNINGS