Question

So I’m trying to write a program that finds the union, intersection, and determining if b is a subset of a for two groups of characters entered.

So if I enter

abcd for a[]

and

ac for b[]

It should print:

intersection: ac

union: abcd

“b is a subset of a”.

My code is working for the most part, but my union function isn’t giving an output. Do you have any suggestions for fixing it? I ran through it and it seems to be executing, but d isn’t printing for someone… is my boolean statement wrong?

My code:

#include <stdio.h>
#include "simpio.h"
#include "genlib.h"
#include "strlib.h"

#define n 26


/* typedef enum letters {a,b,c,d,e,f,g,h,i,j,k,l,m,n,o,p,q,r,s,t,u,v,w,x,y,z};
letters letter; */


bool intersection(bool a[], bool b[], bool c[]);
void GetSet(bool set[]);
void init(bool a[]);
void printArray(bool set[]);
void getunions(bool a[], bool b[], bool d[]);
void contain(bool a[], bool b[]);

main()
{
      bool a[n], b[n], c[n], d[n]; 
      init(a);
      init(b);
      init(c); /* intersection */
      init(d); /* union */
      printf("Entries for a = \n");
      GetSet(a);
      printf("Entries for b = \n");
      GetSet(b);
      intersection(a,b,c);
      printArray(c);
      getunions(a,b,d);      
      printArray(d);
      contain(a,b);
      getchar();      
}

void init(bool set[])
{
     int i;
     for(i=0;i<n;i++)
     {
                     set[i]=FALSE;
     }
}

void GetSet(bool set[])
{
     int i;
     string str=GetLine();
     int len=StringLength(str);
     for(i=0;i<len;i++)
     {
                       set[str[i]-97]=TRUE;
     }
}


bool intersection(bool a[], bool b[], bool c[])
{
    int i;
    for(i=0;i<n;i++)
    {
           if(b[i]&&a[i]==TRUE) c[i]=TRUE;
    }
    printf("\n\nThe intersection is\n");
    return c;
}

void getunions(bool a[], bool b[], bool d[])
{
     int i;
     for(i=0;i<n;i++)
     {
                     if(a[i]==TRUE||b[i]==TRUE) 
                     d[i]==TRUE;
     }
}


void printArray(bool set[])
{
     int i;
                for(i=0;i<n;i++)
                {
                                if(set[i]) 
                                printf("%c", i+97);
                }

}

void contain(bool a[], bool b[])
{
     int i;
     bool flag;
     for(i=0;i<n;i++)
     {
                     if(a[i]&&b[i]) flag=TRUE;
     }
     if(flag) printf("\n\nb is a subset of a.\n");
     else printf("\n\nb is not a subset of a.\n");
}

Answer 1

In getunions, d[i]==TRUE; should be d[i]=TRUE;. You want an assignment, not a comparison.

As an aside, I think the contain function is incorrect. A) it does not initialize flag, and B) it says “b is a subset of a” as long as a and b share at least one common element.