Why Does a Prefix Zero Turn 0123 into 83 in C/C ?

Numeric Constants and the Mystical Power of Prefix Zero

Have you ever wondered what happens when you prefix a numeric constant in C/C with a zero? Unlike the familiar decimal constants (e.g., 123), it seems that this seemingly innocuous modification holds a hidden secret.

To illustrate this strange behavior, consider the example in the original question: initializing an int with the value 0123. Intriguingly, the printed result is not 123 as one might expect but an unexpected 83. What's going on under the hood that transforms this seemingly decimal number into something different?

The answer lies in the enigmatic world of numeric constants, where the prefix zero holds an ancient power. By default, numeric literals in C/C are assumed to be decimal (base 10). However, if you prefix them with a zero, they magically transform into octal constants, signaling the compiler to interpret them using base 8.

In the case of 0123, each digit is interpreted according to the octal system, yielding the following calculation:

0 = 0
1 = 1
2 = 2
3 = 3

Combining these values in groups of three, we get:

012 = 0 8^2 1 8 2 = 66
3 = 3

Adding these two values gives us the final result: 66 3 = 83.

This explains the unexpected behavior observed with prefixed zeroes. It's a testament to the intricate intricacies of C/C , where hidden mechanics can reveal surprising and often confusing results. So, next time you encounter a numeric constant prefixed with zero, remember the octal door it opens, allowing your compiles to traverse the path less traveled.

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