Help with array union and intersection

[tw02]

I am trying to write a program that reads in two arrays of integers representing the elements of two sets from two different user-specified input files and calculates both the union and the intersection of the two sets. Use arrays to contain the input sets and build both the union and intersection. Both union and intersection must not contain duplicates. Here are the input files:

inputA. dat 0, 1, -3, 5, -11, 6, 8, 9, 11, 17, 15, 7, 4, 12

inputB. dat 0, -1, 3, 7, -6, 16, 5, 11, 12, 4, 21, 13

Here is what I have so far. Am I on the right track? Or not even close? Any help is appreciated, thank you.

#include <iostream>
#include <ifstream>
#include <string>
using namespace std;

int main() {
int i(0), j(0), num, num2, arraya[i], arrayb[j];//declare and initialize variables
string filename, filename1;

ifstream input ("inputA.dat");

cout<<"Enter the name of the first input file"<<endl;//first input file from user
cin>>filename;
input.open(filename.c_str());

if (input.fail()) {
cerr<<"Could not open file";//if file cannot be opened
exit(1);
}

input>>num;

while(!input.eof()) {//read numbers from file

arraya[i]=num;

i++;

input>>num;

}

cout<<"Array 1: "<<arraya[i]<<endl;//first array output

ifstream input1 ("inputB.dat");

cout<<"Enter the name of the second input file"<<endl;//second input from user
cin>>filename1;
input1.open(filename1.c_str());

if (input1.fail()) {
cerr<<"Could not open file";//if file cannot be opened
exit(1);
}

input1>>num2;

while(!input1.eof()) {//read numbers from file

arrayb[j]=num2;

j++;

input1>>num2;

}

cout<<"Array 2: "<<arrayb[j]<<endl;//second array output

for (int startindex=0; startindex<i; startindex++) {//step through each number of array
int smallestindex=startindex;//smallest number

for (int currentindex=startindex+1; currentindex<i; currentindex++) {//begin at startindex+1
if(arraya[currentindex]<arraya[smallestindex])
smallestindex=currentindex;//if new small number is found
}

swap(arraya[startindex], arraya[smallestindex]);//swap beginning and smallest numbers
}

cout<<"Sorted Array 1: "<<arraya[startindex]<<endl;//output sorted array

for (int startindex1=0; startindex1<j; startindex1++) {//step through each number of array
int smallestindex1=startindex1;//smallest number

for (int currentindex1=startindex1+1; currentindex1<j; currentindex1++) {//begin at startindex+1
if(arrayb[currentindex1]<arrayb[smallestindex1])
smallestindex1=currentindex1;//if new small number is found
}

swap(arrayb[startindex1], arrayb[smallestindex1]);//swap beginning and smallest numbers
}

cout<<"Sorted Array 2: "<<arrayb[startingindex1]<<endl;//output sorted array

//find union of arrays
int h(0), arrayu[];


for(int k=0; k<i; k++){

arrayu[h] = arraya[i];

h++;

}


for(int k=0; k<j; k++){

arrayu[h] = arrayb[j];

h++;

}

for (int startindex2=0; startindex2<h; startindex2++) {//step through each number of array
int smallestindex2=startindex2;//smallest number

for (int currentindex2=startindex2+1; currentindex2<h; currentindex2++) {//begin at startindex+1
if(arrayu[currentindex2]<arrayu[smallestindex2])
smallestindex2=currentindex2;//if new small number is found
}

swap(arrayu[startindex2], arrayu[smallestindex2]);//swap beginning and smallest numbers
}


return 0;
}

[treuss]

With 10 posts, I would assume you have seen a hint that code should be formatted in code tags.

[Paul McKenzie]

Originally Posted by tw02

I am trying to write a program that reads in two arrays of integers representing the elements of two sets from two different user-specified input files and calculates both the union and the intersection of the two sets. Use arrays to contain the input sets and build both the union and intersection. Both union and intersection must not contain duplicates.

As treuss says, please use code tags when posting code.

First, the "real-world" C++ program to do this is around 4 lines using set_intersection() and set_union(), and they work with arrays of numbers. Your assignment didn't say not to use these functions.

Secondly, if you can't use those functions, you should learn to write your own functions, and not shove everything into main(). Writing programs as you've done makes the program much harder to maintain and debug. In addition, how you get the data is not important when you initially write the code. The "you must read from an input file" instructions that you get from teachers does nothing but wastes a students time in getting the important part of the assignment done. Believe me when I say that.

Here is a sample of how you should have started writing the assignment.

void get_union(int *set1, int size_set1, int *set2, int size_set2, int *output)
{
   //... fill in output with the union of set1 and set2
}

void get_intersection(int *set1, int size_set1, int *set2, int size_set2, int *output)
{
   //... fill in output with the intersection of set1 and set2
}

int main()
{
    int array1[] = {-1, 10, 20};
    int array2[] = {10, 20};
    int output[3];
    get_union(array1, 3, array2, 2, output);
}

Note that there is no fancy I/O, reading from a file, etc. The only thing you see is a function to do the real work of the assignment given to you. You need to write these functions and test to see if they work. Once they work, then you spend your remaining time doing input from a file -- it makes no sense wasting time on the file reading stuff, and you have no idea if the set intersection/union code even works or not.

Regards,

Paul McKenzie

[laserlight]

Originally Posted by Paul McKenzie

First, the "real-world" C++ program to do this is around 4 lines using set_intersection() and set_union(), and they work with arrays of numbers. Your assignment didn't say not to use these functions.

You may also need to use std::sort and std::unique since those functions work on sorted ranges, and your requirements require distinct elements in the final result.

[nuzzle]

Originally Posted by tw02

//output sorted array

You don't need to sort the arrays. You just scan the arrays repeatedly and consider what to do with each element.