>>521
#include <stdio.h>
#include <ctype.h>
char str[] = "SAMPLE ex305.c";
int main(void)
{
char *p = str;
while(*p != '\0'){
if(islower(*p)) *p = toupper(*p);
else if(isupper(*p)) *p = tolower(*p);
p++;
}
printf("%s\n", str);
return 0;
}