A C Puzzle in C Programming?

C programming puzzles are small but tricky coding problems designed to challenge and enhance understanding of the C programming language through creative solutions.

Problem Statement

We are given two numbers, and our task is to combine them in such a way that the second integer is placed before the first integer, resulting in a single combined integer. However, we are not allowed to use any logical, arithmetic, string-related operations, or any pre-defined functions.

Consider the following input/output scenarios to understand the puzzle statement better −

Scenario 1

<b>Input:</b> 12, 54

<b>Output:</b> 5412

<b>Explanation:</b>
Here, the second integer 54 is placed before the first integer 12,
resulting in the output as a single combined integer <b>5412</b>.

Scenario 2

<b>Input:</b> 48, 96

<b>Output:</b> 9648

<b>Explanation:</b>
Here, the second integer 96 is placed before the first integer 48,
resulting in the output as a single combined integer <b>9648</b>.

Puzzle Solution Using Token-Pasting Operator

To solve this puzzle in C, we will use the Token-pasting operator (##). The Token-pasting operator is a preprocessor operator in C that is used with a macro to concatenate two tokens into a single token during compile time.

A macro is a name defined using the #define preprocessor directive. It is used to define constant values or pieces of code that can be reused in a program.

Syntax

#define macro_name(token1, token2) token2##token1

Algorithm

Here is the algorithm for combining two tokens using the Token-pasting operator −

• Define a macro named merge using #define and pass two tokens, a and b.
• Use the token-pasting operator (##) inside the macro to combine the two tokens by placing token b before a.
• In main() function, call the macro and pass the required integers, then print the result.

Example: Basic Token Pasting

Here is the implementation of the puzzle solution using the Token-pasting operator ?

#include <stdio.h>

#define merge(a, b) b##a

int main() {
    printf("Result 1: %d<br>", merge(12, 54));
    printf("Result 2: %d<br>", merge(48, 96));
    printf("Result 3: %d<br>", merge(432, 23));
    return 0;
}

Result 1: 5412
Result 2: 9648
Result 3: 23432

How It Works

Key Points

• The token-pasting operator works at compile time, not runtime.
• It creates a new token by literally joining the characters of two tokens.
• Both tokens must be valid identifiers or numeric literals for proper concatenation.
• The resulting token must form a valid C token (identifier, number, etc.).

Conclusion

The token-pasting operator (##) provides an elegant solution to combine integer tokens without using arithmetic or string operations. This preprocessor feature demonstrates the power of C's macro system in creating compile-time solutions for creative programming challenges.