Palindrome Number in C

Loops

Compare a number with its reversed digits to recognize numeric palindromes.

Complete program

#include <stdio.h>

int main(void) {
    int original, remaining, reversed = 0;
    printf("Number (0 to 999999): ");
    if (scanf("%d", &original) != 1 || original < 0 || original > 999999) return 1;
    remaining = original;
    do {
        reversed = reversed * 10 + remaining % 10;
        remaining /= 10;
    } while (remaining);
    puts(original == reversed ? "Palindrome" : "Not a palindrome");
    return 0;
}

Try in Circuit →

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How it works

Keep the original value because the digit-extraction loop consumes its working copy. Comparing the final reversed value with the original answers the question.

This definition treats input as a nonnegative number, not a text string: leading zeroes are discarded during conversion. Try 0, 121, and 120. A word palindrome needs string indexing and possibly rules for capitalization and spaces.

Sample input

1221

Enter these values when prompted. The transcript below includes typed responses.

Expected output

Number (0 to 999999): 1221
Palindrome

Concepts to practice

• Preserving state
• Equality
• Digit loops

Predict a different input or change one value, then compare the result with your prediction. Keep changes within the documented bounds and read warnings before trusting an answer.