Step by Step solution about How to resolve the algorithm Walk a directory/Non-recursively step by step in the C programming language

The C program uses regular expressions to walk a directory and print the names of files that match a given pattern.

• It includes the necessary header files for directory operations, regular expressions, and input/output.
• The walker function takes two arguments: the directory to walk and the regular expression pattern to match against filenames.
• It uses regcomp to compile the regular expression pattern and opendir to open the specified directory.
• It then iterates through the directory entries using readdir, and for each entry, it uses regexec to check if the filename matches the pattern.
• If there's a match, the filename is printed using puts.
• After processing all the entries in the directory, it closes the directory using closedir and frees the compiled regular expression pattern using regfree.
• The main function calls walker to walk the current directory (.) and print the names of files that end with .c.

#include <sys/types.h>
#include <dirent.h>
#include <regex.h>
#include <stdio.h>

enum {
    WALK_OK = 0,
    WALK_BADPATTERN,
    WALK_BADOPEN,
};

int walker(const char *dir, const char *pattern)
{
    struct dirent *entry;
    regex_t reg;
    DIR *d; 

    if (regcomp(&reg, pattern, REG_EXTENDED | REG_NOSUB))
        return WALK_BADPATTERN;
    if (!(d = opendir(dir)))
        return WALK_BADOPEN;
    while (entry = readdir(d))
        if (!regexec(&reg, entry->d_name, 0, NULL, 0))
            puts(entry->d_name);
    closedir(d);
    regfree(&reg);
    return WALK_OK;
}

int main()
{
    walker(".", ".\\.c$");
    return 0;
}