diff --git a/src/stringManipulation.c b/src/stringManipulation.c
index 37c9f89..84eea0a 100644
--- a/src/stringManipulation.c
+++ b/src/stringManipulation.c
@@ -67,17 +67,33 @@ unsigned int power(unsigned int base, unsigned int exponent){
 	}
 }
 
+bool everyCharacterIsDigit(char *string)
+{
+	bool onlyDigits = true;
+	for(int i=0;*(string+i)!='\0';++i){
+		if(*(string+i)<'0'||*(string+i)>'9'){
+			onlyDigits = false;
+			break;
+		}
+	}
+	return onlyDigits;
+}
+
+
 unsigned int toUnsignedInteger(char *ID)
 {
+	if(everyCharacterIsDigit(ID)){
 	unsigned int result = 0;
 	int IDLength = strlen(ID);
 	for(int i=0, j = IDLength - 1;i<IDLength;++i,--j){
 		result += (*(ID+j) - '0') * power(10,i);
 	}
-	return result;
+		return result;
+	} else {
+		return 0;
+	}
 }
 
-
 char *generateCheckString(unsigned int customerID, char *customerPassword)
 {
 	char *IDString = to_string(customerID);
diff --git a/src/stringManipulation.h b/src/stringManipulation.h
index 22781a2..82e39cb 100644
--- a/src/stringManipulation.h
+++ b/src/stringManipulation.h
@@ -1,9 +1,10 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
-#include <math.h>
+#include <stdbool.h>
 char *stringConcatenation(char *, char *);
 char *to_string(int);
 char *generateCheckString(unsigned int, char *);
 unsigned int toUnsignedInteger(char *);
 unsigned int power(unsigned int, unsigned int);
+bool everyCharacterIsDigit(char *);