Thread: incompatible types in assignment

following is main function of my program

Code:

#include<stdio.h>
#include"header.h"

main()
{
    unsigned char crc;
    unsigned char ar;
    pdt pv;
    adt av;
    frame *f1;
    frame fr;
    
    int src1=0;
    int dest1=1;

    av.ack=9;
    
//opens a file and assigns a file descriptive to fp
    fp=fopen("txtfile","r");

   //generates stuffed information
   stuff(&pv,fp);
   
    //creates the control byte
    control_byte(&pv);

    //crc is generated for the information
    crc=crc_gent(&pv);

    //frame is created..
    f1=(frame *)make_frame(&pv,crc,src1,dest1);
    
    //push that frame into a buffer
    push(f1);
    
//check for the acknowledgement from the receiver side
    ar=ack_check(&av);

//sliding window is created...
    fr = slide(512,ar); //incompatibe type in assignment
}

my header file is

Code:

#include<stdio.h>
//typedef int frame_type;

FILE * fp;

typedef struct payload {
	int frm_typ;
	unsigned char cb;
	unsigned char stuf_info[5];
}pdt;

typedef struct frame {
	char st_flag;
	int src_addr;
	int dest_addr;
	pdt p;
	unsigned char crc;
	char end_flag;
}frame;
struct frame f4[512];

typedef struct ack_frme
{
char st_flg;
int src_addr;
int dest_addr;
unsigned char ack;
char end_flg;
}adt;

i have problem in
fr = slide(512, ar);


slide function is returning a frame..
but for that line its giving error as incompatible types in assignment.