Modifying a program to run as command line arguments in C - c

Question

Full disclosure, this is an assignment for a class I have to do. We have a program that checks if two words are anagrams. We are supposed to modify it so that we can enter the words as command lines in a program. For instance: (./a.out hello elloh: is an anagram... ./a.out hello world: Not an anagram).
Here is the original program:
#include <stdio.h>
#define N 26
int main()
{
char ch;
int letter_counts[N]= {0};
int i;
int count =0;
printf("enter a word: ");
while((ch=getchar())!= '\n')
{
letter_counts[ch - 'a']++;
}
for(i =0;i<N;i++)
printf("%d", letter_counts[i]);
printf("enter the second word: ");
while((ch=getchar())!= '\n')
{
letter_counts[ch - 'a']--;
}
for(i =0;i<N;i++)
printf("%d", letter_counts[i]);
for(i =0;i<N;i++)
if(letter_counts[i]==0)
count++;
if(count == N)
printf("The words are anagrams.\n");
else
printf("The words are NOT anagrams.\n");
return 0;
}
Now here is what I have so far:
#include <stdio.h>
#define N 26
/*
This program is a modified version of anagram.c so that the words run as command-line arguments.
*/
int main(int argc, char *argv[])
{
if(argc != 3)
{
printf("Incorrect number of arguments");
return 0;
}
char ch;
int letter_counts[N]= {0};
int i;
int count =0;
//int k;
//for (k = 1; i < argc; i++)
//{
while((ch=getchar())!= '\n')
{
letter_counts[ch - 'a']++;
}
for(i =0;i<N;i++)
printf("%d", letter_counts[i]);
while((ch=getchar())!= '\n')
{
letter_counts[ch - 'a']--;
}
//for(i =0;i<N;i++)
//printf("%d", letter_counts[i]);
for(i =0;i<N;i++)
if(letter_counts[i]==0)
count++;
int k;
int j;
for (k = 1; i < argc; i++)
{
for (j = 0; j < N; j++)
{
if (count == N)
{
printf("%s and %s are anagrams\n", argv[k], argv[k + 1]);
break;
}
else
printf("The words are NOT anagrams. \n");
}
}
if(count == N)
printf("The words are anagrams.\n");
else
printf("The words are NOT anagrams.\n");
//}
return 0;
}
The output (if the number of arguments is correct) is always :
0000000000000000000000000
0000000000000000000000000
These are anagrams
What am I doing wrong here and what is the best way to go about this?
Thank you for any help I really appreciate it.

Answer 1

You are using getchar() which reads from STDIN, which isn't what you want to do if you're getting your words from command-line arguments. Instead you want to look at argv:
for (char *c = argv[1]; *c != NULL; c++) {
letter_counts[*c - 'a']++;
}
and
for (char *c = argv[2]; *c != NULL; c++) {
letter_counts[*c - 'a']--;
}
More about argc and argv: http://crasseux.com/books/ctutorial/argc-and-argv.html

Answer 2

To not solve your homework for you I'll show you how to use argc and argv on a different program that just checks if the first parameter reversed equals the second:
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
int main(int argc, char **argv)
{
if (argc != 3) {
printf("Usage: %s first_word second_word\n\n", argv[0]);
return EXIT_SUCCESS;
}
char const *first = argv[1];
char const *second = argv[2];
size_t first_length = strlen(first);
size_t second_length = strlen(second);
if (first_length != second_length) {
puts("The words are NOT semordnilaps.\n");
return EXIT_SUCCESS;
}
for (size_t first_index = first_length, second_index = 0; first_index; --first_index, ++second_index) {
if (first[first_index - 1] != second[second_index]) {
puts("The words are NOT semordnilaps.\n");
return EXIT_SUCCESS;
}
}
puts("The words are semordnilaps.\n");
}

Answer 3

Modified program torun from command line argumement. Below is working code snippet for you.
Here we pass two command line arguments with program name. while ((ch = argv[1][len]) != '\0') retrieve the char by char from first arguments and while ((ch = argv[2][len]) != '\0') retrieve the same from the second and rest of the logic remains same.
#include <stdio.h>
#define N 26
int main(int argc, char *argv[])
{
if( argc != 3)
{
printf("Incorrect argumemts\n");
return 0;
}
char ch;
int letter_counts[N]= {0};
int i;
int count =0;
int len=0;
while ((ch = argv[1][len]) != '\0')
{
letter_counts[ch - 'a']++;
len++; /* moving index */
}
for(i =0;i<N;i++)
printf("%d", letter_counts[i]);
len=0;
while ((ch = argv[2][len]) != '\0')
{
letter_counts[ch - 'a']--;
len++; /* moving index */
}
for(i =0;i<N;i++)
printf("%d", letter_counts[i]);
for(i =0;i<N;i++)
if(letter_counts[i]==0)
count++;
if(count == N)
printf("The words are anagrams.\n");
else
printf("The words are NOT anagrams.\n");
return 0;
}