Question

How to find all 4 digits numbers that are palindrome in base 10 and base 2 with C

Answer 1

#include <stdio.h>
#include <string.h>
#include <stdbool.h>

char* strrev(char* str) {
    char *p1, *p2;
 
    if (!str || !*str)
        return str;
 
    for (p1 = str, p2 = str + strlen(str) - 1; p2 > p1; ++p1, --p2) {
        *p1 ^= *p2;
        *p2 ^= *p1;
        *p1 ^= *p2;
    }
 
    return str;
}

void toBinary(unsigned int number, char binaryNumber[]) {
    int i = 0;
 
    while (number != 0) {
        binaryNumber[i] = (number % 2) + '0';
        i++;
        number /= 2;
    }
 
    strrev(binaryNumber);
}
 
int isBinaryRepresentationOfNumberPalindrome(unsigned int number) {
    char binaryNumber[17] = "";
 
    toBinary(number, binaryNumber);
 
    char revBinaryNumber[17] = "";
    strcpy(revBinaryNumber, binaryNumber);
    strrev(revBinaryNumber);
 
    return strcmp(binaryNumber, revBinaryNumber) == 0;
}
 
bool isPalindrome(int n) {
    int reverse = 0, temp = n;
 
    while (temp != 0) {
        int remainder = temp % 10;
        reverse = (reverse * 10) + remainder;
        temp = temp / 10;
    }
 
    return n == reverse;
}
 
int main(void) {
 
    for (int i = 1000; i < 10000; i++) {
        if (isPalindrome(i) && isBinaryRepresentationOfNumberPalindrome(i)) {
            char binaryNumber[17] = "";
            toBinary(i, binaryNumber);
 
            printf("%d %s\n", i, binaryNumber);
        }
    }
 
    return 0;
}
 
 
 
 
 
/*
run:
 
7447 1110100010111
9009 10001100110001
 
*/

 

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