Converting numbers randomly puts negative values

Projects Programming
1

Im putting a 32 bit file in an array and the number is not as expected and when I multiply an unsigned char I end up with a negative number!!!!

ino file
const unsigned char Serialno[]={9,72,69,15,81};
volatile uint32_t SerialNoInt;
void setup() {

// put your setup code here, to run once:
Serial.begin(9600);
Serial.println(Serialno[0]*100000000);
Serial.println(Serialno[1]*1000000);
Serial.println(Serialno[2]*10000);
Serial.println(Serialno[3]*100);
Serial.println(Serialno[4]);
SerialNoInt=
Serialno[0]*100000000+Serialno[1]*1000000+Serialno[2]*10000+Serialno[3]*100+Serialno[4];
Serial.println(SerialNoInt);
}
void loop() {
// put your main code here, to run repeatedly:

}

Result
900000000
72000000
-30896
1500
81
971970685

2

Force the compiler to use unsigned math.

Serial.println(Serialno[0]*100000000UL);

3

Not just unsigned but force the long int calculation, so the L at the end of the numbers is super important Serial.println(Serialno[0]*100000000U[b][color=red]L[/color][/b]);

If you don’t force the use of a long value, the compiler defaults to an int and will perform the computation using 2 bytes (on a 8 bit arduino) instead of 4 which will drive the behavior You see