How do i clear the array - c++

Question

I am trying to write a program that can read a string from Serial Monitor Input and count the size of characters as the input data and store the input to the array, but i have some trouble that the Serial monitor will remain the last input data for example if I input ABC it will show "Size of input data = 3 characters" then i input ABC again it will remain the last data that i input before, I already reset it =0 what mistake do i make?
Serial monitor showing:
Please input
Size of input data = 3 characters
ABC
Please input
Please input
Size of input data = 7 characters
ABC
ABC
here's my code:
String Msg ;
char buf[1200]={0} ; // this is an array
char input;
int num=0;
void setup() {
// Initialize serial and wait for port to open:
Serial.begin(115200);
while (!Serial)
{
; // wait for serial port to connect. Needed for native USB port only
}
}
void loop() {
while (Serial.available())
{
input = (char)Serial.read();
if(input != '\n' )
{
buf[num] = input;
Msg+=input;
num++;
}
else{
buf[num++] = input; // last character is newline
buf[num] = 0; // string array should be terminated with a zero
Serial.println("Please input");
Serial.print("Size of input data = ");
Serial.print(Msg.length());
Serial.print(" characters");
Serial.println("");
Serial.println(Msg);
Serial.println("Please input");
Serial.println("");
Serial.println("");
for(int i=0; i<num ;i++){
Msg[i]=0;
buf[i] =0;
}
}
num=0;
}
return;
}

Answer 1

According to the Arduino manual the String [] operator does the same as charAt().
As there is also a setCharAt() function I suppose [] and charAt() are read only.
The manual doesn't say that but why would they have a setCharAt() then.
Just assign an empty string to Msg to clear it.
Msg = "";

Answer 2

You are doing it in the wrong way.
Msg is a String type variable, not an array so you can just clear string like below.
Msg="";
Don't use unnecessary for loop to clear a char buf array you can do it in a better way by using the memset function.
memset(buf, 0, sizeof(buf));
and finally, take "num=0;" inside else loop so that it will be zero once completion not every time while loop is executing.
So final tested code will look like this,
String Msg ;
char buf[1200] = {0} ; // this is an array
char input;
int num = 0;
void setup() {
// Initialize serial and wait for port to open:
Serial.begin(9600);
while (!Serial)
{
; // wait for serial port to connect. Needed for native USB port only
}
}
void loop() {
while (Serial.available())
{
input = (char)Serial.read();
if (input != '\n' )
{
buf[num] = input;
Msg += input;
num++;
}
else {
buf[num++] = input; // last character is newline
buf[num] = 0; // string array should be terminated with a zero
Serial.println("Please input");
Serial.print("Size of input data = ");
Serial.print(Msg.length());
Serial.print(" characters");
Serial.println("");
Serial.println(Msg);
Serial.println("Please input");
Serial.println("");
Serial.println("");
Msg ="";
memset(buf, 0, sizeof(buf));
num = 0;
}
}
return;
}