C 小写字母编程大写并输出

main()
{
FILE *fp;
char str[100],filename[10];
int i=0;
if((fp=fopen("test","w"))==NULL) //
{
printf("cnnot open file\n");
exit(0);

}
printf("lease input a string:\n");
gets(str);
while(str[i]!='!')
{
if(str[i]>='a'&&str[i]<='z')
str[i]=str[i]-32;
//str[i]=(str[i]-32);
fputc(str[i],fp);
i++;
}
fclose(fp);
fp=fopen("test","r");
fgets(str,strlen(str)+1,fp);
printf("%s\n",str);
fclose(fp);

return 0 ;
}