Line delete function

src/CustomerData.txt

@@ -1,6 +1 @@
-1234=example
-ID=1234
-forename=Max
-Surname=Mustermann
-password=example
-balance=0
+balance=500

src/TempData.txt

@@ -0,0 +1,5 @@
+1234=example
+ID=1234
+forename=Max
+Surname=Mustermann
+balance=0

src/updateCustomerAccountBalance.c

@@ -0,0 +1,95 @@
+#include "updateCustomerAccountBalance.h"
+#include "currentCustomerAccountBalance.c"
+
+void deleteLineFromFile(int line){
+    FILE *fptr1, *fptr2;
+    char file1[] ="CustomerData.txt";
+    char file2[] ="TempData.txt";
+    char curr;
+    int del=line, line_number = 0;
+    fptr1 = fopen(file1,"r");
+    fptr2 = fopen(file2, "w");
+    curr = getc(fptr1);
+    if(curr!=EOF) {line_number =1;}
+    while(1){
+      if(del != line_number){
+        putc(curr, fptr2);
+        curr = getc(fptr1);
+        if(curr =='\n') line_number++;
+        if(curr == EOF) break;
+      }else{
+        
+      }
+
+    }
+    fclose(fptr1);
+    remove(file1);
+    fclose(fptr2);
+    rename(file2,"CustomerData.txt");
+    
+}
+
+void replaceBalanceInString(float replacementBalance, int currentLine) {
+    deleteLineFromFile(currentLine-1);
+    printf("deleting from line %i. balance will be replaced with %f", currentLine, replacementBalance);
+    char newBalanceLine[MAX_LENGTH] = "balance=";
+    char balance_as_string[MAX_LENGTH];
+    sprintf(balance_as_string, "%g", replacementBalance); //converts replacement balance to string
+    strcat(newBalanceLine, balance_as_string);
+    printf(newBalanceLine);
+
+    char buffer[MAX_LENGTH];
+    FILE *file = fopen("CustomerData.txt", "w"); 
+
+    for(int i=0;i<currentLine;i++){
+        fgets(buffer, MAX_LENGTH, file);
+    }
+    fprintf(file, newBalanceLine);
+    fclose(file);
+}
+
+bool updateAvailableAccountBalance(int user_id, float changeInBalance){
+
+    bool keep_reading = true;
+    float availableBalance = 0;
+
+    char buffer[MAX_LENGTH];
+    char stringID[MAX_LENGTH] = "ID=";
+    char user_id_as_string[MAX_LENGTH];
+    char balance_String[MAX_LENGTH];
+    int currentLine=0;
+
+    sprintf(user_id_as_string, "%d", user_id); // converts user_id to string
+    strcat(stringID, user_id_as_string);
+
+    FILE *file = fopen("CustomerData.txt", "r+"); 
+
+    while(keep_reading) {
+        fgets(buffer, MAX_LENGTH, file);
+        currentLine++;
+        if (feof(file)) {
+            keep_reading = false;
+        }
+        else if(strstr(buffer, stringID)) { //found the customer
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            fgets(buffer, MAX_LENGTH, file);
+            strcpy(balance_String, buffer);
+            currentLine+=4;
+            availableBalance = fetchBalanceFromBalanceString(balance_String);
+            replaceBalanceInString(availableBalance+changeInBalance,currentLine);
+            keep_reading = false;
+        }
+
+    }
+    fclose(file);
+}
+
+int main(){
+
+    updateAvailableAccountBalance(1234,500);
+    return 0;
+
+}
+

src/updateCustomerAccountBalance.h

@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define MAX_LENGTH 100
+bool updateAvailableAccountBalance(int user_id, float changeInBalance);
+void deleteLineFromFile(int lineNumber);
+void replaceBalanceInString(float replacementBalance, int currentLine);