system
January 13, 2014, 7:00pm
1
Hi there,
I've got a problem with if-statements:
My problem: I want to compare values from an array to predefined values so that I can print a special message for every case. My code:
x=Str1[8], HEX;
y=Str1[7], HEX;
z=Str1[6], HEX;
a=Str1[5], HEX;
if(x=="5D" && y=="92" && z=='C6' && a=='42')
{lcd.print("xxx");}
The values themselves are from an array that is filled earlier. When I try to compile my code it says: "ISO C++ forbids comparison between pointer and integer" How can I realize that comparison?
Thanks in advance.
system
January 13, 2014, 7:06pm
2
x=Str1[8], HEX;
This is NOT doing what you think it is. Loose the , HEX crap.
My problem: I want to compare values from an array
It would be good to know what kind of array.
If the array is a char array, then no element in the array can hold "5D". An element might, depending on the array type, hold '5D'.
I suggest that you head over to http://snippets-r-us.com for help with your snippets.
You are assigning with the value of HEX in all cases.
In the C and C++ programming languages, the comma operator (represented by the token ,) is a binary operator that evaluates its first operand and discards the result, and then evaluates the second operand and returns this value (and type); there is a sequence point between these evaluations.
The use of the comma token as an operator is distinct from its use in function calls and definitions, variable declarations, enum declarations, and similar constructs, where it acts as a separator.
The comm...
Making up your own language is never a good idea.
An int can never be "5D". use 0x5D as a constant.
system
January 13, 2014, 7:26pm
6
An int can never be "5D". use 0x5D as a constant.
For better understanding my problem here's my full code:
include <SoftwareSerial.h>
#include <LiquidCrystal.h>
LiquidCrystal lcd(6, 9, 5, 1, 3, 0);
SoftwareSerial rfid(7, 8);
SoftwareSerial xbee(10, 9);
//Prototypes
void check_for_notag(void);
void halt(void);
void parse(void);
void print_serial(void);
void read_serial(void);
void seek(void);
void set_flag(void);
//Global var
int flag = 0;
int Str1[11];
char x;
char y;
char z;
char a;
//INIT
void setup()
{
lcd.begin(16, 2);
lcd.setCursor(0, 0);
lcd.print(" Wilkommen!");
xbee.begin(9600);
rfid.begin(19200);
delay(10);
halt();
}
//MAIN
void loop()
{
read_serial();
}
void check_for_notag()
{
seek();
delay(10);
parse();
set_flag();
if(flag = 1){
seek();
delay(10);
parse();
}
}
void halt()
{
//Halt tag
rfid.write((uint8_t)255);
rfid.write((uint8_t)0);
rfid.write((uint8_t)1);
rfid.write((uint8_t)147);
rfid.write((uint8_t)148);
}
void parse()
{
while(rfid.available()){
if(rfid.read() == 255){
for(int i=1;i<11;i++){
Str1[i]= rfid.read();
}
}
}
if(!rfid.available()) {lcd.setCursor(0,1); lcd.print("Chip auflegen");}
}
void print_serial()
{
if(flag == 1){
//print to serial port
lcd.setCursor(0, 1);
x=Str1[8];
y=Str1[7];
z=Str1[6];
a=Str1[5];
if(x=="5D" && y=="92" && z=='C6' && a=='42')
{lcd.print("xxx");}
//lcd.print(Str1[8], HEX);
//lcd.print(Str1[7], HEX);
//lcd.print(Str1[6], HEX);
//lcd.print(Str1[5], HEX);
//lcd.print(" ");
delay(1000); //
check_for_notag();
}
}
void read_serial()
{
seek();
delay(10);
parse();
set_flag();
print_serial();
delay(100);
}
void seek()
{
//search for RFID tag
rfid.write((uint8_t)255);
rfid.write((uint8_t)0);
rfid.write((uint8_t)1);
rfid.write((uint8_t)130);
rfid.write((uint8_t)131);
delay(10);
}
void set_flag()
{
if(Str1[2] == 6){
flag++;
}
if(Str1[2] == 2){
flag = 0;
}
}
if(x==0x5D && y==0x92 && z==0xC6 && a==0x42)
P.S. Call your variables sensible names - single letter names are useless in describing what is going on.
P.S. Furthermore, x,y,z,a are all only used in one function, so why waste memory, make them local.
system
January 13, 2014, 7:47pm
8
Unfortunately it only shows the Tag-ID only executes the following part:
lcd.print(Str1[8], HEX);
lcd.print(Str1[7], HEX);
lcd.print(Str1[6], HEX);
lcd.print(Str1[5], HEX);
lcd.print(" ");
Why is that and how to resolve it?
system
January 13, 2014, 7:50pm
9
Thanks for your help, Tom. I replaced my if-statement by yours but it only shows the Tag-ID.
system
January 13, 2014, 7:51pm
10
An int can never be "5D".
But an "int" can be 'SD', interestingly.
TCWORLD
January 13, 2014, 7:54pm
11
In which case one or all of the following are not true:
What exactly does this:
display on the LCD?
system
January 14, 2014, 11:45am
13
What exactly does this:
display on the LCD?
was a rhetoric question. It was designed to make you THINK about what you are doing vs. what you are seeing. Str1[n] contains a value. You are printing that value to the LCD using a specific method with specific arguments.
You should experiment with different values for those arguments to see what affect that has on the output. For instance, use DEC, OCT, and BIN as the second argument. Then, for giggles, use 7 as the second argument.
Note that in all cases, WHAT is being printed has not changed. The result has though. Do you know why?
When you do, then you can understand why your questions in this whole thread make no sense.
system
January 14, 2014, 2:55pm
14
I can see that the result was converted into the specified number system. But how does that affect my plan to compare it to a special value and print a special text?
system
January 14, 2014, 3:02pm
15
But how does that affect my plan to compare it to a special value and print a special text?
The VALUE never changed. The output representation did.
if(Str[8] == 0x5D)
{
// Do something when Str[8] contains 0x5D
}
system
January 14, 2014, 3:09pm
16
if(Str[8] == 0x5D)
The VALUE never changed. The output representation did.
But isn't that 0x5D wrong then? I tried the following:
if(x==93 && y==142 && z==185 && a==66)
{lcd.setCursor(0,1);
lcd.print("xxx");}
but it didn't work either. Why is that?
KeithRB
January 14, 2014, 3:45pm
17
because you are getting twisted up between strings and integers.
str[8] is a character, like '5' or 'D', it cannot be "5D" because that is two characters. To convert you would need to do something like
x = convert_chars_to_byte(str[8]) + 16 * convert_chars_to_byte(str[7]);
system
January 14, 2014, 3:48pm
18
Hi KeithRB,
+ 16 * convert_chars_to_byte(str[7])
So can I sum up all the str[x]? And for what does "+ 16*" stand for?
Thanks
system
January 14, 2014, 4:09pm
19
Hi KeithRB,
unfortunately your code doesn't work. It says "rfid_aktuell.ino: In function 'void print_serial()':
system
January 14, 2014, 5:24pm
20
str[8] is a character,
First, it's Str, not str. Second, Str is an array of ints. Pay attention.