number_and_its_square_with_all_different_digits.c

/*

    number_and_its_square_with_all_different_digits.c

    Task:
    There is a three digit number. Its square is a six digit number.
    Find all three-digit numbers that have all the different digits
    in them and each square.
    For example, 567 is a three digit number. Its square 567*567 = 321489.
    We know that 5, 6, 7 and 3, 2, 1, 4, 8, 9 are all 9 different digits.


    You can find all my C programs at Dragan Milicev's pastebin:

    https://pastebin.com/u/dmilicev

*/

#include <stdio.h>

void ShowArray( char text[], int array[], int n )
{
    int i;

    printf("%s", text);

    for(i=0;i<n;i++)
        printf("%2d", array[i]);

    printf("\n");
}

// returns 1 if all elements are distinct (unique, different from each other)
// otherwise returns 0
int all_array_elements_are_distinct( int arr[], int size )
{
    int i, j;

    for (i=0; i<size; i++)
        for (j=i+1; j<size; j++)
            if (arr[i] == arr[j])
                return 0;

    return 1;
}

// extract digits from number into array digits[]
// returns the number of extracted digits
int extract_digits_from_number( int number, int digits[20] )
{
    int i, j, number_of_digits = 0, mem;

    while( number != 0 )
    {
        digits[number_of_digits++] = number % 10;   // fill array digits[]
        number = number / 10;
    }

    // reverse first number_of_digits elements of array digits[]
    for ( i=0, j=number_of_digits-1; i<number_of_digits/2; i++, j-- )
    {
        mem = digits[i];
        digits[i] = digits[j];
        digits[j] = mem;
    }

    return( number_of_digits );
} // extract_digits_from_number

// Concatenates two integer arrays arr1[] and arr2[] into arr3[] and
// returns number of integers of arr3
int concatenateTwoArrays(int arr1[], int n1, int arr2[], int n2, int arr3[], int *n3)
{
    int i;

    *n3 = 0;

    for(i=0;i<n1;i++)
        arr3[(*n3)++] = arr1[i];

    for(i=0;i<n2;i++)
        arr3[(*n3)++] = arr2[i];


    return (*n3);
}

// Enter a three-digit number, returns entered num
int inputThreeDigitsNumber(int *num)
{
    int ch;

    while(1)
    {
        printf("\n Enter a three-digits number: ");
        scanf("%d", num);
        while ( ( ch = getchar() ) != '\n' );   // empty the input buffer of a stream

        if( *num>99 && *num<1000 )
            return *num;
        else
            printf("\n Entered number is not a three-digits number. Try again. \n");
    }
}


int main(void)
{
    int i, num, count=0;
    int numDigits[3], squareDigits[6], allDigits[9];
    int numLen, squareLen, allLen;

    // Let's test above functions
    inputThreeDigitsNumber(&num);
    printf("\n num = %d \t num^2 = %d \n", num, num*num);

    numLen = extract_digits_from_number(num, numDigits);
    ShowArray("\n numDigits =   ",numDigits,numLen);

    squareLen = extract_digits_from_number(num*num, squareDigits);
    ShowArray("\n squareDigits =      ",squareDigits,squareLen);

    concatenateTwoArrays(numDigits, numLen, squareDigits, squareLen, allDigits, &allLen);   // or
    //allLen = concatenateTwoArrays(numDigits, numLen, squareDigits, squareLen, allDigits, &allLen);
    ShowArray("\n allDigits =   ",allDigits,allLen);

    // Let's find such numbers
    for(i=100;i<1000;i++)
    {
        numLen = extract_digits_from_number(i,numDigits);
        squareLen = extract_digits_from_number(i*i, squareDigits);
        concatenateTwoArrays(numDigits, numLen, squareDigits, squareLen, allDigits, &allLen);

        if( all_array_elements_are_distinct(allDigits,allLen) )
        {
            count++;
            printf("\n %2d. \t i = %3d \t i^2 = %6d \n", count, i, i*i );
        }
    }

    printf("\n There are %d such numbers. \n", count );

    return 0;

} // main()