--- joko/Uni/BSArch/01/prime.c	2006/05/12 19:03:04	1.3
+++ joko/Uni/BSArch/01/prime.c	2006/05/12 20:38:15	1.5
@@ -1,33 +1,55 @@
+/* $Id: prime.c,v 1.5 2006/05/12 20:38:15 joko Exp $ */
+
 #include <stdio.h>
-#define PRINTPRIME(x) if(prime(x)) printf("%i\n", x)
 
-int prime(int number)
+#define PRINTPRIME(x) if(is_prime(x)) printf("%i\n", x)
+#define PRINTERROR(message) fprintf(stderr, "ERROR: %s\n", message)
+
+/* check for prime number */
+int is_prime(int number)
 {
-  int i;
-  for(i=2;i*i<=number;i++){
-  	if((number%i) == 0)
-	  return 0;
-  }
-  return 1;
+	int i;
+	for (i=2; i*i <= number; i++) {
+		if ((number % i) == 0)
+			return 0;
+	}
+	return 1;
 }
 
 int main(int argc, char * argv[])
 {
-	int i, j;
-	FILE * fp;
-	char num[11];
-	if(argc > 2 ){
-		j=atoi(argv[2]);
-		for(i=atoi(argv[1]) ; i< j; i++){
+	
+	if (argc == 1) {
+		PRINTERROR("No arguments given, will segfault under cygwin. :-)");
+		return -1;
+	}
+	
+	/* (3) range mode */
+	if (argc > 2) {
+		int i, j;
+		j = atoi(argv[2]);
+		for (i = atoi(argv[1]); i< j; i++) {
 			PRINTPRIME(i);
 		}
-	}else {
-		fp=fopen(argv[1], "r");
-		if(fp==NULL){
+	
+	/* other modes */
+	} else {
+
+		/* try to open file for reading */
+		FILE * fp = fopen(argv[1], "r");
+		
+		/* (1) test-single-number mode: first argument is not a filename */
+		if (fp == NULL) {
 			PRINTPRIME(atoi(argv[1]));
-		}else{
-			while(fgets(num, 11, fp))
+		
+		/* (2) file mode: read numbers from file */
+		} else {
+			char num[11];
+			while (fgets(num, 11, fp)) {
+				printf("raw: %s\n", num);
+				printf("num: %i\n", atoi(num));
 				PRINTPRIME(atoi(num));
+			}
 			fclose(fp);
 		}
 	}