diff --git a/du1/program.c b/du1/program.c
index 175aa30..5c2e1ab 100644
--- a/du1/program.c
+++ b/du1/program.c
@@ -1,5 +1,6 @@
 #include <stdio.h>
 #include <ctype.h>
+#include <string.h>
 
 int main (){
 	char c[100];
@@ -30,11 +31,11 @@ int main (){
 			for(int i = 0; i < 100; i++){
 				if(c[i] == '\n') break; 
 				if(isupper(c[i]))
-					printf(tolower(c[i]));
+					printf("%c", tolower(c[i]));
 				else if(islower(c[i]))
-					printf(toupper(c[i]));
+					printf("%c", toupper(c[i]));
 				else
-					printf(c[i]);
+					printf("%c", c[i]);
 			}
 		}
 	//counter++;