C programming automatic octal interpretation

Question

Code 1:

int a = 0987654321;
printf(\"%d\",a);

Code 2:

int a;
scanf(\"%d\",&a);
printf(\"%d\",a);

Here if

Answer 1

There are multiple representations which you can use when writing code with C -

• Hexadecimal (0x123A)
• Binary (0b1011) -- Is not supported by standard C but is an extension provided by compilers like gcc.
• Octal (01237)
• Decimal (1234) -- perhaps the most common.

What you are using here is the octal representation (because it starts with a 0). Meaning each of the digit is base 8. As a result each of the digit after the 0 can only be in the range [0-7]. 9 is not a valid octal digit and hence the compiler is complaining.

If you want to actually use the decimal representation you can remove the 0 as -

int a = 987654321;

In the second example it actually works fine because scanf with %d always scans as a decimal representation and 9 is a valid decimal digit.