Question

I have code that loops through numbers and creates the character array representation of that integer. So for a number like 1234 I get an array that looks like {‘1’, ‘2’, ‘3’, ‘4’}

Part of the code is shown below:

do {
   //print here
     c[i++] = (char)(((int)'0')+(num - (num/10)*10 ));
} while ((num = num/10) != 0);

I am having an issue when it comes to large data types like long long int: 18446612134627563776

I printed the values in the loop are:

18446612134627563776
18446730879801352832
18446742754318731738
...
18446744073709551615

The values should be

18446612134627563776
1844661213462756377
184466121346275637
...
18
1

The strange thing is that the loop terminates. The last printed value is 18446744073709551615 != 0, so not sure why it terminated there. I think its some issue with the data type that i am not doing right.

This is the print statement:

printk("long=%llu sec=%llu , char=%c\n", num, (num/10)*10, (char)(((int)'0')+((num - (num/10)*10 ))));

Answer 1

long long int: 18446612134627563776

long long int is a signed type, usually 64 bits wide, with the maximal representable number

2^63-1 = 9223372036854775807

Your value is larger than that, and overflows, probably to

2^63 - 18446612134627563776 = -131939081987840

The printed values are

2^64 + (-131939081987840)/(10^k)

Change the type to unsigned long long to get the expected results.