Printing all variants of a word - c

Question

So here is the the program which i am trying to make:
Create password generator, which uses dictionary and match files to generate passwords by replacing letters in the dictionary words with their matches.
Example:
Dictionary file:
apple
loop
Match file:
a 4
e 3
o 0
Output:
4pple
appl3
4ppl3
l0op
lo0p
l00p
And this is my solution:
#include <stdio.h>
#include <string.h>
/* function prototypes */
int read_source(char* ,char* ,char* );
char* shift_string(char* ,char* );
int write_shifted(char* ,char* );
int main(int argc, char *argv[])
{
/* argv[1]: the source file with the original strings
* argv[2]: the shift file which indicates which characters are to be
* replaced with what
* argv[3]: the file in which the new strings are to be stored*/
if(!argv[1])
{
printf("No source file, can do nothing. Exiting.\n");
return 1;
}
else if (!argv[2])
{
printf("No shift file given, can do nothing. Exiting.\n");
return 2;
}
else if (!argv[3])
{
/* If no output file has been specified, print the
* output directly to the console. */
read_source(argv[1],argv[2],NULL);
return 0;
}
if (read_source(argv[1],argv[2],argv[3])!=0)
{
printf("There has been an error. Exiting.\n");
return 3;
}
if (argv[3])
{
printf("Everything seems to have gone according to plan.\n");
printf("Your output has been stored in \"%s\"\n",argv[3]);
}
return 0;
}
int read_source(char* source_file,char* shift_file,char* out_file)
{
FILE *file_pointer;
file_pointer=fopen(source_file, "r");
/* Exit gracefully if source_file cannot be found. */
if (file_pointer == NULL)
{
printf("Couldn't open \"%s\" for reading.\n",source_file);
return 1;
}
char* new_line;
/* maximum line length, can be changed if needed */
char line[256];
/* Go through the source file. */
while (fgets(line,sizeof line,file_pointer) != NULL)
{
new_line = shift_string(shift_file,line);
if (new_line==NULL)
{
printf("There has been an error with replacing the characters.\n");
return 2;
}
write_shifted(new_line,out_file);
}
int fclose(FILE *file_pointer);
return 0;
}
char* shift_string(char* shift_file,char* source_string)
{
/* This function replaces certain characters in a given source_string as
* specified by shift_file */
/* Open shift file. */
FILE *file_pointer;
char i,j;
file_pointer=fopen(shift_file, "r");
/* Exit gracefully if shift_file cannot be found. */
if (file_pointer == NULL)
{
printf("Couldn't open \"%s\" for reading.\n",shift_file);
return NULL;
}
int k;
/* Determine how long the source_string is for the loop below. */
int length = strlen(source_string);
while (fscanf(file_pointer, "%c %c\n", &i, &j)==2)
{
/* This loop actually does the replacing. */
for (k=0;k<length;k++)
{
if (source_string[k]==i)
{
source_string[k]=j;
}
}
}
int fclose(FILE *file_pointer);
return source_string;
}
int write_shifted(char* new_line,char* out_file)
{
/* This function writes the new strings to out_file
* If no out_file has been given, it will write the
* output to the console.*/
if (out_file==NULL)
{
printf("%s",new_line);
return 0;
}
FILE *file_pointer;
/* Open in a+ mode. If out_file does not yet exist, it will be created.
* If it does exist, it will be appended to instead of overwritten. */
file_pointer = fopen(out_file,"a+");
/* Write the new line */
fprintf(file_pointer,"%s",new_line);
fclose(file_pointer);
return 0;
}
So the problem is that now it prints only the final states (4ppl3 l00p) but i also need the middle states (4pple appl3 l0op lo0p). Can someone give me some clues how to make it. thanks in advance. :)

Answer 1

recursion works well for this type of problem. Basically, take whether or not to have the first letter substituted, and recurse with the rest of the word for each case - substituted and not substituted. Do this until you don't have any letters left, and you'll have all your combinations.
// terribly pseudo-codey, but should give the idea
string='abc';
stringfunction("", string);
// simplified, just shifts each letter by one
stringfunction(processed, unprocessed)
if unprocessed is empty
print processed
return
stringfunction(strcat(processed, unprocessed[0]), unprocessed[1]);
stringcunction(strcat(processed, unprocessed[0]+1), unprocessed[1]);
this will print out abc, abd, acc, acd, bbc, bbd, bcc, bcd
of course, for your case, instead of shifting the letter, you'd either do or not do the substitution.