Implementation of function stringConcatenation() and creation of docs.txt to as a documentation for the functions.

src/StringManipulation.c

@@ -1,5 +1,33 @@
 #include "StringManipulation.h"
 /*Code written by Julius Philipp Engel, fdai7057*/
+
+char *stringConcatenation(char *string_1, char *string_2)
+{
+	int lengthStringOne = strlen(string_1);
+	int lengthStringTwo = strlen(string_2);
+	
+	if(lengthStringOne==0||lengthStringTwo==0){
+		printf("Empty strings are not allowed. Aborting.\n");
+		exit(-1);
+		//call error();
+	}
+	
+	const int totalLength = lengthStringOne + lengthStringTwo + 1;
+	char *result = calloc(totalLength, sizeof(char));
+	int i,j;
+	for(i=0,j=0;i<totalLength;++i){
+		if(i<lengthStringOne){
+			*(result+i) = *(string_1+i);
+		}else{
+			*(result+i) = *(string_2+j);
+			++j;
+		}
+	}
+	*(result+i) = '\0';
+	return result;
+}
+
+
 char *to_string(int number)
 {
 	if(number==0)
@@ -28,10 +56,6 @@ char *to_string(int number)
 
 char *generateCheckString(int customerID, char *customerPassword)
 {
-	/*The purpose of this function is to generate a string that is needed when a user wants to login.
-	 * This string is searched for in the customer-data file and if it is found, the login is successful. 
-	 * This function is needed when a new user is created because then it is written in the file for the first time.
-	 * The format of the string is: [ID]=[PASSWORD]*/
 	char *IDString = to_string(customerID);
 	int IDLength = strlen(IDString);
 	int passwordLength = strlen(customerPassword);

src/StringManipulation.h

@@ -1,5 +1,6 @@
 #include <stdlib.h>
 #include <stdio.h>
 #include <string.h>
+char *stringConcatenation(char *, char *);
 char *to_string(int);
 char *generateCheckString(int, char *);

src/docs.txt

@@ -0,0 +1,14 @@
+char *stringConcatenation(char string_1*, char string_2*):
+
+This function takes two char pointers. In this function a new string is created. This new string is the concatenation of string_1 and string_2. The size of the new string is the length of string_1 plus the length of string_2 plus one for '\0'. This function is needed when creating an unique check string for a customer.
+
+char *to_string(int number):
+
+This function takes an integer variable as its argument. It returns an string that contains the digits of number. For example to_string(176) would return "176\0". This function is needed to write data in form of characters into the customer file. 
+
+
+char *generateCheckString(int customerID, char *password): 
+
+The purpose of this function is to generate a string that is needed when a user wants to login. This string is searched for in the customer-data file and if it is found, the login is successful. This function is needed when a new user is created because then it is written in the file for the first time. 
+The format of the returned string is [ID]=[PASSWORD]. 
+For example generateCheckString(177,"tree") would return "177=tree\0".