Understanding the ??!??! Sequence in C

Last update on December 20 2024 13:15:21 (UTC/GMT +8 hours)

Understanding ??!??! in C: Explanation and Example Code

In C language, the sequence ??!??! is not a standard operator but rather a series of trigraph sequences. Trigraphs are a set of three-character sequences that represent certain characters in C, typically for compatibility with keyboards that lack certain symbols. Trigraphs were more relevant historically and are rarely used today, but they are still valid in the language. Let’s explore what ??!??! translates to in C.

Explanation of Trigraphs in C:

In C, trigraphs allow certain symbols to be represented using three-character sequences that start with two question marks (??). The specific trigraphs relevant here are:

• ??! translates to |
• ??= translates to #
• ??' translates to ^

In our case, ??!??! would be translated by the compiler to ||, the logical OR operator.

Example:

Here’s a code snippet that uses ??!??! in a simple conditional expression to check two conditions using the logical OR operation.

Code:

#include <stdio.h> 
int main() {
    int x = 100;
    int y = 200;

    // Using ??!??! as a trigraph equivalent to ||
    if (x ??!??! y) {
        printf("One of the conditions is true.\n");
    } else {
        printf("Both conditions are false.\n");
    }
    return 0;
}

Output:

One of the conditions is true.

Explanation:

In the above example -

• ??!??! is translated by the compiler to ||.
• The if statement checks if either x or y is true using the logical OR operation.

Since y is 1 (true), the condition x ??!??! y evaluates to true, and the if block is executed.