Thread: Beginner with C, need help to understand

Hello together

I'am Maurizio and beginner on language C, but on me Linux/Unix envoirments it's realy good, if i can write meny little help features.

Here i will try to add any Array, and understand Array :-)

Explain my view.
1. open the file GoodIP.txt, read, here i have a lot of IP inside
and this ammount change change every day.

2. Here the reading IP Addresses will be store to my array "Folder" varible "max"

3. printout to screen, to see if this ammount of Addresses are on the right way since here.

Code:

#include <stdio.h>
void main()
{
    // 1. read file GoodIP.txt
    FILE *myFile;
    myFile = fopen("GoodIP.txt", "r");

    // 2. read into array
     int score[max];
        for (i = 0; i < max; i++)

    {
    // 3. Print GoodIP from Array
        printf("Number is: %d\n\n", max[i]);
    return 0;
    }
}

my goal:
5. open file "bannlist.txt", and delete this here the IPaddresses,
that are inside in the "GoodIP.txt"

6. close and save

7. restart Service "systemctl restart fail2ban"

this code will be compile with gcc, on Debian.
Thanks meny time, for reciving any answer.
Regards
Mauri

Hello Salem
First thanks for your fast answer!

Snip GoodIP

root@mail:/etc/fail2ban# cat GoodIP
015.37.246.220
140.211.11.3
151.248.219.221
151.248.219.221
158.181.117.6
81.221.120.2
82.126.76.252
82.136.87.212
83.164.148.131
91.121.119.198
94.237.32.243
94.237.32.243
94.237.32.243
root@mail:/etc/fail2ban# cat GoodIP | wc -l
69

Snip ip.blacklist

root@mail:/etc/fail2ban# cat ip.blacklist
98.242.146.160
98.242.201.128
98.242.202.130
98.242.204.67
99.38.89.33
99.41.175.38
99.64.183.238
99.7.234.226
99.97.25.108
root@mail:/etc/fail2ban# cat ip.blacklist | wc -l
17002

But from where do the application know, which file this will pick to read?

Code:

#include <stdio.h>
int m
ain()
{
    // 1. read file GoodIP.txt
    FILE *myFile;
    myFile = fopen(argv[1], "r");
 
    // 2. read into array
     int score[max];
        for (i = 0; i < max; i++)
 
    {
    // 3. Print GoodIP from Array
        printf("Number is: %d\n\n", max[i]);
    return 0;
    }
    // 4. Service restart fail2ban
        if [ $? -eq 0 ]; then
        systemctl restart fail2ban
    fi
}

regards
Mauri

I Need to understand more from this langauge, equal C or C++,
Here you can write evrything, but understading and implementing on the right way are a other part.

i see the book "Jumping in to C++" but i don't want Start with "hello world"

Exist here other ways ?