%i vs. %d in C\'s Formatted I/O: What\'s the Difference?

Formatted IO with %i and %d: A Detailed Comparison

When utilizing formatted IO functions like printf and scanf, understanding the subtle differences between format specifiers is crucial. Two common specifiers, %d and %i, can lead to confusion if their distinct behaviors are not fully grasped.

Output: Identical Functionalities

If %i and %d are employed for output purposes (i.e., in printf), there is no noticeable difference between them. Both specifiers will produce the same output, whether it be decimal, hexadecimal, or octal.

Input: Where the Distinction Emerges

However, when using these specifiers for input (i.e., in scanf), a clear distinction arises. %d interprets input as an integer in signed decimal format. This means that numbers like -512 would be properly recognized and assigned negative values.

In contrast, %i defaults to decimal interpretation but exhibits a more flexible nature. It not only handles decimal integers but also accommodates hexadecimal and octal values when preceded by relevant prefixes. For instance, 0x1A would be interpreted as a hexadecimal number, while 023 would be recognized as octal.

Practical Example

Consider the input string "033". If scanf reads this using %d, it will treat it as the decimal integer 33. However, using %i, scanf recognizes the leading 0 as an octal prefix, resulting in the integer 27 being assigned to the variable.

Conclusion

In summary, while %i and %d perform similarly for output in formatted IO functions, they exhibit different behaviors for input. %d restricts input to signed decimal numbers, while %i offers more versatility by accommodating hexadecimal and octal values. Understanding this distinction is essential for accurate input handling in C programs.

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