Rational

#include <stdio.h>

typedef struct
{
    int n;
    int d;
}rational;

void doPositiveDenom ( rational *rat )
{
    if ( rat->d < 0 )
    {
        rat->n *= -1;
        rat->d *= -1;
    }
}

void read ( rational *x )
{
    while ( 1 )
    {
        scanf ( "%d %d", &x->n, &x->d );
        doPositiveDenom ( x );
        if ( x->d )
            break;
        printf ( "Denominator can not be 0.\nTry Again.\n" );
    }
}

int hcf ( int a, int b )
{
    if ( a % b == 0 )
        return b;
    return hcf ( b, a % b );
}

void Simplify ( rational *x )
{
    int gcd = hcf ( x->n, x->d );
    x->n /= gcd;
    x->d /= gcd;
}

void Add ( rational *x, rational y )
{
    x->n = ( x->n * y.d ) + ( x->d * y.n );
    x->d = x->d * y.d;
}

void Sub ( rational *x, rational y )
{
    x->n = ( x->n * y.d ) - ( x->d * y.n );
    x->d = x->d * y.d;
}

void Mul ( rational *x, rational y )
{
    x->n *= y.n;
    x->d *= y.d;
}

void Div ( rational *x, rational y )
{
    x->n *= y.d;
    x->d *= y.n;
}

void Reciprocal ( rational *x )
{
    int t = x->n;
    x->n = x->d;
    x->d = t;
}

int Compare ( rational x, rational y )
{
    int num_x = x.n * y.d, num_y = y.n * x.d;
    if ( num_x < num_y )
        return -1;
    else if ( num_x == num_y )
        return 0;
    else
        return 1;
}

void main ( )
{
    int choice, compare;
    rational result, next;
    printf ( "Enter the first rational number (Numerator first)\n" );
    read ( &result );
    while ( 1 )
    {
        printf ( "1:\tAddition\n2:\tSubtraction\n3:\tMultiplication\n4:\tDivision\n5:\tCompare\n6:\tReciprocal\n7:\tDisplay\n0:\tEXIT\nCHOICE:\t" );
        scanf ( "%d", &choice );
        if ( !choice )
            break;
        if ( choice < 6 )
        {
            printf ( "\nEnter the next rational number (Numerator first)\n" );
            read ( &next );
        }
        switch ( choice )
        {
            case 1:
                Add ( &result, next );
                break;
            case 2:
                Sub ( &result, next );
                break;
            case 3:
                Mul ( &result, next );
                break;
            case 4:
                Div ( &result, next );
                break;
            case 5:
                compare = Compare ( result, next );
                break;
            case 6:
                Reciprocal ( &result );
                break;
            case 7:
                break;
            default:
                printf ( "INVALID CHOICE.\nTRY AGAIN.\n\n" );
                continue;
        }
        Simplify ( &result );
        printf ( "\n" );
        if ( choice == 5 )
        {
            if ( compare == -1 )
                printf ( "%d/%d > %d/%d\n\n", next.n, next.d, result.n, result.d );
            else if ( !compare )
                printf ( "%d/%d = %d/%d\n\n", result.n, result.d, next.n, next.d );
            else
                printf ( "%d/%d > %d/%d\n\n", result.n, result.d, next.n, next.d );
        }
        else
            printf ( "RESULT:\t\t%d/%d\n\n", result.n, result.d );
    }
    printf ( "RESULT:\t\t%d/%d\n", result.n, result.d );
}