diff --git a/Readme.md b/Readme.md
index c3367db..aa67d4f 100644
--- a/Readme.md
+++ b/Readme.md
@@ -1,4 +1,6 @@
 
+[![Donate](https://img.shields.io/badge/Donate-PayPal-green.svg)](https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=58Y36H29935PW&item_name=Support+me+to+continue+developing+features&currency_code=EUR&source=url)
+
 # Arduino SIM800L library
 A smart HTTP & FTP library based on Seeeduino that implements the AT HTTP commands to perform GET and POST requests to a JSON API as well as FTP uploads.
 
@@ -112,3 +114,10 @@ In order to perform a request, the library follows these steps:
 
 - Support of HardwareSerial.
 - Support of more content types, not only JSON (application/json).
+
+
+## Development
+- Lint
+```
+cppcheck --enable=all .
+```
\ No newline at end of file
diff --git a/src/GPRS.cpp b/src/GPRS.cpp
index e1c0422..e396ab4 100644
--- a/src/GPRS.cpp
+++ b/src/GPRS.cpp
@@ -42,7 +42,7 @@ const char CONNECTED[] PROGMEM = "+CREG: 0,1";
 const char ROAMING[] PROGMEM = "+CREG: 0,5";
 const char BEARER_OPEN[] PROGMEM = "+SAPBR: 1,1";
 const char OK[] PROGMEM = "OK";
-const char OK_ PROGMEM = "OK";
+const char OK_ = "OK";
 
 Result openGPRSContext(SIM800 *sim800, const char *apn)
 {
diff --git a/src/Http.cpp b/src/Http.cpp
index 906a8bd..b4dae6c 100644
--- a/src/Http.cpp
+++ b/src/Http.cpp
@@ -73,18 +73,17 @@ Result HTTP::disconnect()
 
 Result HTTP::post(const char *uri, const char *body, char *response)
 {
-
-  Result result = setHTTPSession(uri);
+  Result result;
+  setHTTPSession(uri);
+  
   char buffer[32];
   char resp[16];
 
   unsigned int delayToDownload = 10000;
   sprintf_P(buffer, HTTP_DATA, strlen(body), delayToDownload);
   strcpy_P(resp, DOWNLOAD);
-  if (sendCmdAndWaitForResp(buffer, resp, 2000) == FALSE)
-  {
-    result = ERROR_HTTP_DATA;
-  }
+  
+  sendCmdAndWaitForResp(buffer, resp, 2000);
 
   purgeSerial();
   sendCmd(body);
@@ -106,13 +105,12 @@ Result HTTP::post(const char *uri, const char *body, char *response)
 
 Result HTTP::get(const char *uri, char *response)
 {
-
-  Result result = setHTTPSession(uri);
-  char buffer[16];
-  char resp[16];
+  Result result;
+  setHTTPSession(uri);
 
   if (sendCmdAndWaitForResp_P(HTTP_GET, HTTP_2XX, 2000) == TRUE)
   {
+    char buffer[16];
     strcpy_P(buffer, HTTP_READ);
     sendCmd(buffer);
     result = SUCCESS;
@@ -178,7 +176,7 @@ unsigned int HTTP::readSignalStrength()
 
 Result HTTP::setHTTPSession(const char *uri)
 {
-  Result result;
+  Result result = SUCCESS;
   char buffer[128];
 
   if (sendCmdAndWaitForResp_P(HTTP_CID, OK, 2000) == FALSE)
diff --git a/src/Parser.cpp b/src/Parser.cpp
index 05fc87b..362d509 100644
--- a/src/Parser.cpp
+++ b/src/Parser.cpp
@@ -33,7 +33,7 @@ void parseATResponse(const char *buffer, unsigned int size, unsigned int offset,
   const char *twoPointsPointer = strchr(buffer, ':');
   unsigned int twoPointsIndex = (int)(twoPointsPointer - buffer);
   unsigned int valueStartIndex = twoPointsIndex + offset;
-  for (int i = valueStartIndex; i < valueStartIndex + size; ++i)
+  for (unsigned int i = valueStartIndex; i < valueStartIndex + size; ++i)
   {
     response[i - valueStartIndex] = buffer[i];
     response[i - valueStartIndex + 1] = '\0';
@@ -42,8 +42,8 @@ void parseATResponse(const char *buffer, unsigned int size, unsigned int offset,
 
 void parseJSONResponse(const char *buffer, unsigned int bufferSize, char *response)
 {
-  int start_index = 0;
-  int i = 0;
+  unsigned int start_index = 0;
+  unsigned int i = 0;
   while (i < bufferSize - 1 && start_index == 0)
   {
     char c = buffer[i];
@@ -54,7 +54,7 @@ void parseJSONResponse(const char *buffer, unsigned int bufferSize, char *respon
     ++i;
   }
 
-  int end_index = 0;
+  unsigned int end_index = 0;
   int j = bufferSize - 1;
   while (j >= 0 && end_index == 0)
   {
diff --git a/src/Sim800.cpp b/src/Sim800.cpp
index b0dd05c..ec88888 100644
--- a/src/Sim800.cpp
+++ b/src/Sim800.cpp
@@ -58,8 +58,7 @@ int SIM800::checkReadable(void)
 int SIM800::readBuffer(char *buffer, int count, unsigned int timeOut)
 {
     int i = 0;
-    unsigned long timerStart, timerEnd;
-    timerStart = millis();
+    unsigned long timerStart = millis();
     while (1)
     {
         while (serialSIM800.available())
@@ -73,7 +72,8 @@ int SIM800::readBuffer(char *buffer, int count, unsigned int timeOut)
         }
         if (i > count - 1)
             break;
-        timerEnd = millis();
+
+        unsigned long timerEnd = millis();
         if (timerEnd - timerStart > timeOut)
         {
             break;
@@ -114,8 +114,7 @@ int SIM800::waitForResp(const char *resp, unsigned int timeout)
 {
     int len = strlen(resp);
     int sum = 0;
-    unsigned long timerStart, timerEnd;
-    timerStart = millis();
+    unsigned long timerStart = millis();
 
     while (1)
     {
@@ -131,7 +130,7 @@ int SIM800::waitForResp(const char *resp, unsigned int timeout)
             if (sum == len)
                 break;
         }
-        timerEnd = millis();
+        unsigned long timerEnd = millis();
         if (timerEnd - timerStart > timeout)
         {
             return FALSE;