C语言根据后缀判断文件类型

//判断文件类型为pdf或者word类型
#include<stdio.h>
#include<string.h>
int File(char *Filename);
int main(int argc, char *argv[])
{
	
	  char Filename[40];
	  memset(Filename,0x00,sizeof(Filename));
	  strcpy(Filename,argv[1]);
	  printf("%s",Filename);
	  // NULL => not file type
	  printf("12------%d",File(Filename));
	  
	  if(File(Filename) == 1 ){
	  	printf("The file is  type of word or pdf");
	  	}
	  else{
	  		printf("The file is not  type of word or pdf");
	  	}

}

int File(char *Filename){

	   int flag = 0; // 0->NOT 1->yes
	   char str[6];
	   memset(str,0x00,sizeof(str));
	  //.doc .docx .pdf 
	  if( strncmp(Filename,".doc",4) == 0 || strncmp(Filename,".docx",5) == 0 || strncmp(Filename,".pdf",4) == 0)
	  	{
	  		 printf("line of 31————%s",Filename);
	  		 flag = 0;
	  		 return flag;
	  	}
	  strncpy(str,Filename+(strlen(Filename))-4,4);
	  printf("line of 33————%s",str);
	  if( strncmp(str,".doc",4) == 0 ||strncmp(str,".pdf",4)== 0 )
	  	{
	  		flag = 1;
	  		}
	  
	   memset(str,0x00,sizeof(str));
	   printf("line of 40————%s",str);
	   strncpy(str,Filename+(strlen(Filename))-5,5);
	   if( strncmp(str,".docx",5) == 0  )
	  	{
	  		flag = 1;
	  	} 
     return flag;
}