Printing all duplicate words from a file in C - c

Question

What am I supposed to do in order to print only the duplicated words in a file. I'm a beginner in C.
Here's my code:
#include <stdio.h>
#define max 100
main(){
FILE *fpointer;
char ch[max],str[max][max];
int i = 0,j = 0,count = 0;
int a,b;
fpointer = fopen("1.txt","r");
if(fpointer == NULL){
printf("Error!");
return 0;
}
while(fscanf(fpointer,"%s",ch)!=EOF){
strcat(str[i++],ch);
strcat(str[i++]," ");
count++;
}
for(a=0;a<count*2;a=a+2){
for(b=0;b<count*2;b=b+2){
if(strcmp(str[a],str[b])==0){
printf("%s\n",str[b]);
}
}
}
fclose(fpointer);
return 0;
}
An example of input is "shine little star shine bright in the dark star"
and the output of this program is "shine shine little star star shine shine bright in the dark star star". Please help me to print
only duplicate words. Tnx

Answer 1

In your inner loop, instead of starting at the beginning of the list, start one element after the current one. That way you're not comparing an element against itself or comparing any two elements twice.
for(a=0;a<count*2;a=a+2){
for(b=a+2;b<count*2;b=b+2){ // b=a+2 instead of b=0
if(strcmp(str[a],str[b])==0){
printf("%s\n",str[b]);
}
}
}
Output:
shine
star

Answer 2

Since you wrote duplicate words, i am guessing the words in the file will be repeated twice only.
So you second nested for loop is starting from the beginning every time, and thats where the problem is. You have to make sure that the word already checked is not iterated over again. For that you can change your second for loop a little
for(a=0;a<count*2;a=a+2){
for(b=a+2;b<count*2;b=b+2){ //notice b=a+2
if(strcmp(str[a],str[b])==0){
printf("%s\n",str[b]);
}
}
}
Note
For cases when the words are repeating more then twice, my suggestion would be to use some hashing technique to store if a word has already occurred or not. And then compare and print accordingly.

Answer 3

You have a couple of problems here.
Go through and write some comments. For example, put these where they belong:
// Open the file
// Read in the strings
// Compare the strings
If you do this you will notice you have some problems. For instance, what is this line for?
strcat(str[i++]," ");
It's not reading in a string. So what is it doing?
In your final loop, you want to compare each string with all the others. So obviously, you start with the first string, and you compare it to all the others:
for (a=1; a<count; a++)
if(strcmp(str[0],str[a])==0)
{
printf("%s\n",str[0]);
break;
}
Now we can compare the first string with each following string and print it out if it is duplicated. The "break" is there so we only print it once.
But this only compares the first string with the others. How do we compare all of them? Another loop, of course.
// Compare each string against all the ones after it
for (target=0; target<count; target++)
for (a=target+1; a<count; a++)
// If the strings match AND they are not both null
// (why print out copies of null strings? - nobody wants that)
if(strcmp(str[target],str[a])==0) && strlen(str[a])
{
// Print it
printf("%s\n",str[target]);
// Why is this here?
strcpy(str[a],"");
for (copies=a+1; copies<count; copies++)
if(strcmp(str[copies],str[target])==0)
strcpy(str[copies],"");
// We got a match, stop checking for this string
break;
}
See how we've got one big loop that steps through each string, and a smaller loop that steps through all the remaining strings (no point in stepping through the ones we already looked at).
Now a question for you: why is "strcpy(str[a],"") and the next for loop in there? What purpose do they serve?

Answer 4

This is one way to do it. Please enable warnings - you left out a library header. I've also checked array limits. You need to find a better way to limit the string input too, than just guess a large array size.
#include <stdio.h>
#include <stdlib.h>
#include <string.h> // included header
#define MAX 100
int main(void){ // correct function
FILE *fpointer;
int reported [MAX];
char ch[MAX], str[MAX][MAX];
int index = 0, a;
fpointer = fopen("1.txt","r");
if(fpointer == NULL){
printf("Error!");
return 0;
}
while(fscanf(fpointer,"%s",ch) == 1){ // testing for 1 item read
for(a=0; a<index; a++){
if(strcmp(ch, str[a])==0){
if (reported[a] == 0) // don't report twice
printf("%s ",ch);
reported[a]++;
break;
}
}
if(a >= index) { // check if loop completed
if (index >= MAX) { // check if array is full
printf("\nToo many words read\n");
exit(1);
}
strcpy(str[index], ch); // word was not found
reported[index] = 0;
index++; // keep tabs on array length
}
}
printf("\n",ch);
fclose(fpointer);
return 0;
}
Program output:
shine star

Answer 5

One issue is that you are storing every word, regardless of whether it has already been seen:
while(fscanf(fpointer,"%s",ch)!=EOF){
strcat(str[i++],ch);
strcat(str[i++]," "); // ??? what is this for
count++;
}
Ideally, you'd only like to store each word once, and maintain a count of how often that word appears in the file:
while ( fscanf( fpointer, "%s", ch ) != EOF ) // whitespace is your friend, use it
{
if ( ch_is_not_already_in_str )
{
strcpy( str[count++], ch );
}
else
{
update_count_for_that_string;
}
}
Then at the end, you just loop through ch and print each string that has a count greater than 1.
for ( i = 0; i < count; i++ )
{
if ( str[i]_occurs_more_than_once )
printf( "%s ", str[i] );
}
The bits you need to figure out are ch_is_not_already_in_str, update_count_for_that_string, and str[i]_occurs_more_than_once. How would you go about searching your str array for an occurence of the string in ch? How would you maintain a counter for each string?