Why this weird infinite loop occuring? - loops

Question

I'm writing a arduino serial communication code where I'll send sentence through serial communication like "azyb"+sentence+"byza" where first and second part is to identify my sentence is going to begin and end . My code is here (just giving the loop function as other's working fine) :
void loop()
{
if (Serial.available() > 0)
{
int i=0, j=0, len=0;
char *sentance;
String line = Serial.readString();
len = line.length();
Serial.println(len);
Serial.println(line);
for (; i < len; i++)
if (line[i] == 'a' && line[i+1] == 'z' && line[i+2] == 'y' && line[i+3] == 'b'){
//first if
Serial.println("First");
i += 4;
while (i < len){
sentance[j] = line[i];
i++; j++;
if (line[i+1] == 'b' && line[i+2] == 'y' && line[i+3] == 'z' && line[i+4] == 'a'){
// second IF
Serial.println("Second");
sentance[j] = 'NULL';
encry_flag = true;
i = i + 4;
line = "";
break;
}
}
}
if (!encry_flag){
Serial.println("No code is send");
Write_text("damn "); // to write text in OLED display
}
else{
Serial.println(sentance);
Write_text(sentance); // to disply sentence in OLED display
encry_flag = false;
}
// clear the buffer
while (Serial.available() > 0)
char c= Serial.read();
}
}
But when I send a valid sentence like "azybanklonbyza" which will display "anklon" in OLED display , the code get trapped into a infinite loop which goes till first if condition came true but never run till the second if condition came true,and then circle back which should not be acting like this.
this infinite loop do not check the condition either encry_flag is true or false and never goes to the statement where buffer is being cleared.
From the screenshot you can understand that the for loop and the while loop within the for loop breaks as total strings is printed again and again which is done only once before for loop.
From where this infinite loop is created ? I'm totally lost.
FYI : if "azyb" and "byza" is not added at the beginning and end , the code ran just fine as it never fulfill any if condition. I tried using one character also ( "azybhbyza" to print "h" ) , but the result is same .

Answer 1

I am not familiar with arduino but
if (line[i+1] == 'b' && line[i+2] == 'y' && line[i+3] == 'z' && line[i+4] == 'a')
Should it not start with i ? And I see you used a character pointer "sentance" but you have not initialized it anywhere and as far as I know. The uninitialized pointer might lead to memory corruption depending on compiler memory management. Depending on hardware memory I am also considering the fact that it may corrupt some other memory contents also. Which may explain your variable "i" not reaching the end. Try initializing sentance with some space like
sentance = new char[25];
It may work. And also if you are testing on hardware, it may behave freaky at times.