Convert an int to char array, then append another char

Projects Programming
1

Hi,
I'm trying to convert an int to a char array then append another char on the end. This is to be outputted to an LCD. I keep getting stuck when trying to follow examples on the web.

long number = x;   //value from user input 0 to 2million
char buf[12];         // Output buffer
char suffix[2];       // suffix for appending to number (k or M)
int thousands = (number/1000);
suffix[0] = 'k';
itoa(reducedNo, buf, 10);   // convert number to text
buf+=suffix; //invalid operands to binary operator+

My brain has melted now. Does anyone have a good way to do this without using String?

2

How about using sprintf() ?

long number;
char buffer[12];

void setup() 
{
  Serial.begin(115200);
  
  number = 2000000;
  sprintf(buffer,"%luk",number);
  Serial.println(buffer);

  number = 1;
  sprintf(buffer,"%luk",number);
  Serial.println(buffer);
}

void loop() 
{
}
3 
buf+=suffix; //invalid operands to binary operator+

char arrays can't be concatenated with the + operator. You can use strcat(), although you will need to ensure suffix is a valid c-style string (Needs to be null-terminated, you don't explicitly make it). You can also use sprintf like UKHeliBob suggested, or you can simply do this:

Get the length of the string:

int len = strlen(buf);

"Append" 'k' to the string by replacing the null with your character

buf[len] = 'k';

And setting the next character to be null:

buf[len+1] = '\0;
4

Thanks. Sorry I missed something quite important! :blush:
There should be a line..

float reducedNo = number/1000

And i should have been asking how to convert a float! [facepalm]

So this means sprintf wont work as it does not like floats on the arduino.
itoa also wants an int

Basically what I am trying to do is display a frequency on an LCD that can be anything from 0 to 2 million. I'm hoping to make the larger numbers easier to read by making them look like 10k instead of 10000.

5

It may be just as easy and efficient to just print to the LCD and use a conditionals to select a different format depending on the size of the number.

Something like

if number > 999999 use 1M or 2M
if number > 999 use 1K or 25K
otherwise it's less than 4 digits just output the number

You'll likely need something similar for formatting anyway.

dtostrf() is a function that works well on Arduino for converting floats to string. Might be worth looking up.

6

RichMo:
Basically what I am trying to do is display a frequency on an LCD that can be anything from 0 to 2 million. I'm hoping to make the larger numbers easier to read by making them look like 10k instead of 10000.

I think what you're looking for is dtostrf()

7

Thanks guys. I've used a combination of these in my code to get everything displayed nice.