#include<stdio.h> int main(void) { char ch; printf("input characters:"); ch=getchar( ); while(ch !=' '){ if(ch>='A'&&ch<='Z') ch=ch-'A'+'a'; else if(ch>='a'&&ch<='z') ch=ch-'a'+'A'; putchar(ch); ch=getchar( ); } return 0; }