Question

I am just beginning programming and for my first project, I decided to write a program for finding the greatest common divisor using the Euclidean division algorithm in c.

Now though, I want to extend the problem to save the intermittent quotients, remainders, dividends and divisors so that I can use them.

My thought was that I could add something to the inner loop that would put each of the four variables into one row of the array and then start a new row for the next iteration of the loop.

Here’s what I have so far.

#import <Foundation/Foundation.h>

int main (int argc, const char * argv[])
{

    NSAutoreleasePool * pool =[[NSAutoreleasePool alloc]init];
    NSMutableArray * numberSaver=[[NSMutableArray alloc] init];
    NSNumber * q;
    NSNumber * end;
    NSNumber * or;
    NSNumber * rem;

    int a,b, divisor, dividend, quotient, remainder, temp, gcd, row;

    //get the two numbers
    NSLog(@"of which 2 numbers whould you like the GCD?");
    scanf("%u%u", &a,&b);

    //make the bigger number the dividend, smaller divisor

    if (a>b) {
        dividend=a;
        divisor=b;
    } else {
        dividend=b;
        divisor=a;
    }

    remainder=1;
    row=0;
    while (remainder !=0) {

        quotient=1;
        temp=divisor;

        while (temp<dividend) {
            temp+=divisor;
            ++quotient;
        }
        q=[NSNumber numberWithInt:quotient];
        end=[NSNumber numberWithInt: dividend];
        or=[NSNumber numberWithInt: divisor];
        //set NSNumber objects q, end, or to the integer values at quotient dividend and divisor

        gcd=divisor;
        //This is so that we can save divisor to be the GCD and not change it to 0 before it is printed
        remainder=quotient*divisor - dividend;
        rem=[NSNumber numberWithInt:remainder];
        //point to the remainder as an object

        dividend= divisor;
        divisor= remainder;
        //Get dividend and divisor ready for the next loop

        //I'd like to start adding the newly created NSNumbers to  numberSaver here
        [numberSaver addObject:quotient atIndex:row:0];
    }
    NSLog(@"gcd= %u",gcd);

    [pool drain] ;

    return 0;
}

Answer 1

I’d suggest creating a mutable dictionary with each iteration of the loop and, after adding all the numbers to that, put it into the “master” array:

while (remainder !=0) {

    // Each time through the loop, a new dictionary is created and put
    // into iterationDict; you can then add objects to it.
    NSMutableDictionary * iterationDict = [NSMutableDictionary dictionary];

    // ...

    q=[NSNumber numberWithInt:quotient];
    end=[NSNumber numberWithInt: dividend];
    or=[NSNumber numberWithInt: divisor];

    [iterationDict setObject:q forKey:@"quotient"];
    [iterationDict setObject:end forKey:@"dividend"];
    [iterationDict setObject:or forKey:@"divisor"];

    // etc.
    [numberSaver addObject:iterationDict];
}

Storing these things in a dictionary rather than an array means that you don’t have to remember the order in which you added them (divisor before dividend, e..g). Instead, you access them by the key. Later, you can get the values for any given iteration out of the array:

NSUInteger iteration = 3;
NSNumber * quotient = [[numberSaver objectAtIndex:iteration] objectForKey:@"quotient"];

Please comment if any of this needs explication.