pvjc22/du1/program.c

#include <stdio.h>

int main(){
	int c = 0;
	char a;
	while(1){
		c = getchar();
		if(c == EOF)
			break;
		if (c >= 'a' && c <= 'z')
			c = c - 'a' + 'A';
		else if(c >= 'A' && c <= 'Z') 
			c = c - 'A' + 'a';
		a = c;
		putchar(a);
	}
	return 0;
}