Creating a sequence of numbers from a string of digits C++

Question

I need to make a program where a user inputs a string of numbers.
It then outputs the numbers grouped so that each grouping, separated by a space, is larger than the last when you put the numbers together.
If the remaining digits together equal a sum smaller than the previous grouping they are omitted.
Ex.:
314159265 would output 3 14 15 92
Here: 3 < 14 <15 < 92 but 65 was omitted because it is less than 92

or
9876543210 would output 9 87 654 3210
Here: 9 < 87 < 654 < 3210

It has to do this 5 times with strings 1-20 characters long.

My code works for shorter strings, ie the ones above, but when they are longer than around 12 characters the end output messes up.

Ex.: 98765432101234567898 outputs 9 87 654 3211 12333 instead of 9 81 654 3210 12345 67898 Here: 9 < 87 < 654 < 3211 < 12333 it should output 9 < 87 < 654 < 3210 < 12345 < 67898

I have no idea why it doesn't work with larger strings and any help would be greatly appreciated.

#include<iostream>
#include<iomanip>
#include<math.h>
#include<string>
#include<stdlib.h>

using namespace std;

void input (string &a,string num[20]){
    string numfinal,temp;
    cout<<"Enter the string of numbers: ";
    getline(cin, a);
    int length=a.length();
    for(int i=0;i<length;i++){
        num[i]=a.substr(i,1);
    }

    for(int r=0;r<length;r++){
        int n=atoi(temp.c_str());
        int o=atoi(num[r].c_str());
        int p=temp.length();
        if((length-r<=p)&&(o<n)){
        }
        else if((o>n)||(r==0)){
            temp=num[r];
            numfinal=numfinal+temp+" ";
        }
        else if((o<n)||(o=n)){
            int w=n;
            temp=num[r]+num[r+1];
            n=atoi(temp.c_str());
            if(n<w){
                int a=1;
                int q=r+2;
                while(n<w){
                    temp=temp+num[q];
                    n=atoi(temp.c_str());
                    p++;
                    a++;
                }
                numfinal=numfinal+temp+" ";
                r=r+a;
            }
            else{
                numfinal=numfinal+temp+" ";
                r++;
            }
        }
    }
    cout<<numfinal<<endl;
}

int main(){
    string a;
    string num[20];
    for(int r=0;r<5;r++){
        input(a,num);
    }
    return 0;
}

Is it possible that the first example, 314159265, could produce the output: 31 41 59 265? It seems like there could be many outputs for a single input. And if so, how would you choose which is the 'correct' output? — Obicere
– Obicere, Commented Feb 8, 2017 at 21:47
atoi has a number of failure cases you are not checking. stoi or strtol may be better choices. — user4581301
– user4581301, Commented Feb 8, 2017 at 21:53
@Obicere The first digit is supposed to stand by itself. Sorry i didn't include that. — Uncblueguy
– Uncblueguy, Commented Feb 8, 2017 at 21:57
I tried 3141592653589793238 no zeroes and it still screwed up the end, outputting 3 14 15 92 653 5899 9322 . I also tried stoi and it gives the "Not declared in this scope" error code — Uncblueguy
– Uncblueguy, Commented Feb 8, 2017 at 22:06

Sam Mokari · Accepted Answer · 2017-02-08 22:54:26Z

1

This code works. But do not forget that write a simple code and use the new style of C++ programming.

#include <vector>
using namespace std;
vector<string>  Input( )
{
    string a;
    cin >> a;
    vector<string> num;
    string current("-1");
    string str;
    for(auto c : a)
    {
        str.append(1, c);
        if (stoi(str) > stoi(current) )
        {
            num.push_back(str);
            current = str;
            cout << str << " ";
            str = "";
        }
    }
    cout << endl;
    return num;
}

int main() {
    for (int i = 0; i<5; i++) {
        vector<string> num;
        num = Input();
    }
    return 0;
}

answered Feb 8, 2017 at 22:54

Sam Mokari

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2 Comments

Uncblueguy Over a year ago

Thank you for the help but I have to use old c++ and can't really follow what's happening in this code, I don't know what auto is or push_back(str) does.

Sam Mokari Over a year ago

You can use a simple array instead of vector and use char instead of auto. Easy!!!

Justin Hellreich · Accepted Answer · 2017-02-08 22:03:52Z

0

Looks like you are missing a q++ in your while loop:

while(n < w) {
   temp = temp + num[q];
   n = atoi(temp.c_str());
   p++;
   a++;
   q++;
}

This is why the ~~fourth~~ third digit was being copied over.

The maximal munch algorithm might give you some inspiration on a cleaner way to solve this problem. It is meant for tokenizing but it may help. Good luck!

answered Feb 8, 2017 at 22:03

Justin Hellreich

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4 Comments

Uncblueguy Over a year ago

Thank you, the q++ helped, now it works fiine until the strings are over 6 groupings long, then it just doesnt output any thing over the sixth grouping.

Justin Hellreich Over a year ago

Yes, it seg faults because your num array is too small. Increasing the array size is a quick and dirty fix but do consider using vectors to avoid this issue. Also, just a suggestion: using more descriptive variable names will aid both you and anyone in debugging.

Uncblueguy Over a year ago

Sorry, but I'm not following. I didn't make a num array it is a string? Increasing the string size will have no effect.

Justin Hellreich Over a year ago

Well actually it is an array of strings (which probably isn't necessary since you could just use a single string). As I said, a quick fix would be to just increase the size (I bumped it to 40 to check), but this really isn't a good solution. See Sam's solution for a well thought out method.

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