crc-wroking

#include<stdio.h> #include<string.h> #define N strlen(g) char t[28],cs[28],g[]="10001000000100001"; int a,e,c;

void xor(){

for(c = 1;c < N; c++) 
	cs[c] = (( cs[c] == g[c])?'0':'1'); 

}

void crc(){

for(e=0;e<N;e++) 
	cs[e]=t[e]; 
do{ 
   if(cs[0]=='1') 
   	   xor(); 
   for(c=0;c<N-1;c++) 
   	   cs[c]=cs[c+1]; 
   cs[c]=t[e++]; 
}while(e<=a+N-1); 

}

int main() {

  printf("\nEnter data : "); 
  scanf("%s",t); 
  printf("\n----------------------------------------"); 
  printf("\nGeneratng polynomial : %s",g); 
  a=strlen(t);    
  for(e=a;e<a+N-1;e++)  
  	t[e]='0'; 
  	
  printf("\n----------------------------------------"); 
  printf("\nModified data is : %s",t); 
  printf("\n----------------------------------------"); 
  
  crc(); 
  printf("\n CRC checksum is : %s",cs); 
  
  for(e=a;e<a+N-1;e++) 
  	t[e]=cs[e-a]; 
  printf("\n----------------------------------------"); 
  printf("\nFinalcodeword transmitted is : %s",t); 
  printf("\n----------------------------------------"); 
  printf("\nTest error detection 0(yes) 1(no)? : "); 
  scanf("%d",&e); 
  
  if(e==0){ 
	  do{  
		  printf("\nEnter the position where error is to be inserted : "); 
		  scanf("%d",&e); 
	  }while(e==0 || e>a+N-1); 

	  t[e-1]=(t[e-1]=='0')?'1':'0'; 
	  
	  printf("\n----------------------------------------"); 
	  printf("\nErroneous data : %s\n",t);     
  } 
  
  crc(); 
  
  for(e=0;(e<N-1) && (cs[e]!='1');e++); 
  
  
  if(e<N-1)  { 
		printf("\n CRC checksum is : %s",cs); 
		printf("\nError detected\n\n");         
  } 
  else{ 
		printf("\n CRC checksum is : %s",cs); 
		printf("\nNo error detected\n\n"); 
  } 
  printf("\n----------------------------------------\n"); 
  return 0; 	

}