How do I create a max function in c++ to search for the max in a sequence of numbers

Question

I've done it with arrays before in java, but I'm having trouble trying to convert it to work with my current code. I'm still new to C++ and am also looking for some critique. My code that works looks like a mess and would like suggestions on how to make it look neater. I'm trying to get into the habit of writing my contracts first then writing the codes. (Which is honestly helping me understand what I'm doing better). I mean, it's not clean. I want to clean it afterward for sure, but I want to try fixing this portion. I would just like some suggestions. I'm going to be working on this some more.

// This program takes a user defined number 'n'
// and runs it through a function that returns 
// the number that follows 'n' in hailstone sequence.
// Since there is no number that follows 1 in the sequence,
// this function requires its parameter 'n' to be greater
// than 1. 

/* example output
What number shall I start with?  7
The hailstone sequence starting at 7 is:
7 22 11 34 17 52 26 13 40 20 10 5 16 8 4 2 1
The length of the sequence is 17.
The largest number in the sequence is 52.
The longest hailstone sequence starting with a number up to 7 has length 17
The longest hailstone sequence starting with a number up to 7 begins with 7
*/

#include <algorithm>
#include <cstdio>
using namespace std;

int main(int argc, char** argv)
{ 
    int n;

// hailLength will keep track of how many
// numbers are produced in the sequence.

    int hailLength = 1; 

    printf("What number shall I start with? ");
    scanf("%d", &n);
    printf("The hailtone sequence starting at %d is: \n", n);

    printf("%i", n);
    printf(" ");

// While 'n' is not equal to 1 the function will calculate whether 'n' is even 
// then it will divide n/2, otherwise it will compute 3n + 1 if n is odd. 

    while(n != 1)
    {
        if(n % 2 == 0)
        {
            n /= 2;
            printf("%i", n);
            printf(" ");
        }
        else
        {
            n = (3 * n) + 1;
            printf("%i", n);
            printf(" ");
        }
        hailLength++;

    }
    printf("\n");
    printf("The length of the sequence is %i.", hailLength);
    printf("\n");

// This line will display the largest value in the hailstone sequence.
// This portion is also broken.

    int maximum(int n);
    {
        int k = 0;
        int ans = n;
        while(k != n)
        {
            k++;
            if(ans < k)
            {
                ans = k;
            }
        }
        //return ans;
        printf("%u", ans);
        //printf("%u", k);
        printf("\n");
    }


//printf("The largest number in the sequence is %i", max(n));
return 0;
}

Answer 1

You could do something like this to find the max.

#include <algorithm>    // std::max
int maxNumSoFar = n;

while( n != 1 ) {
    maxNumSoFar = std::max(n, maxNumSoFar);

    if( n%2 == 0) n /= 2;
    else n = 3*n+1
}

printf("Max number seen is %d", maxNumSoFar);

Also since you are working in C++ and not C you might want to look into "cin" and "cout" for your I/O instead of using C's "printf" and "scanf".

Answer 2

There's no reason to:

1. generate your list first.

2. save that list somewhere, as is your apparent intent.

3. and after generating the entire list and printing it, go back and then figure out what was the largest number in itself.

Doing it this way is certainly possible, and it's not rocket science, but it's still unnecessarily complicated. It's much simpler to simply keep track of the largest number seen...

int max;

... at the same time you're generating the list.

That's it. Let's begin:

scanf("%d", &n);
printf("The hailtone sequence starting at %d is: \n", n);

max=n;

You start the ball rolling by setting max to the first number. It's obvious that this is the largest number seen, so far.

Then, in your existing for loop, after you compute the next number, and display it, check it against the current value of max:

    }

    if (n > max)
         max=n;

    hailLength++;

Then, when your loop terminates, you will find the largest number in the sequence, in max, already.