Port scanner code in c

portscanner.c

#include "stdio.h"
#include "sys/socket.h"
#include "errno.h"
#include "netdb.h"
#include "string.h"
#include "stdlib.h"
 
int main(int argc , char **argv)
{
    struct hostent *host;
    int err, i , sock ,start , end;
    char hostname[100];
    struct sockaddr_in sa;
     
    //Get the hostname to scan
    printf("Enter hostname or IP : ");
    gets(hostname);
     
    //Get start port number
    printf("\nEnter start port number : ");
    scanf("%d" , &start);
     
    //Get end port number
    printf("Enter end port number : ");
    scanf("%d" , &end);
 
    //Initialise the sockaddr_in structure
    strncpy((char*)&sa , "" , sizeof sa);
    sa.sin_family = AF_INET;
     
    //direct ip address, use it
    if(isdigit(hostname[0]))
    {
        printf("Doing inet_addr...");
        sa.sin_addr.s_addr = inet_addr(hostname);
        printf("Done\n");
    }
    //Resolve hostname to ip address
    else if( (host = gethostbyname(hostname)) != 0)
    {
        printf("Doing gethostbyname...");
        strncpy((char*)&sa.sin_addr , (char*)host->h_addr , sizeof sa.sin_addr);
        printf("Done\n");
    }
    else
    {
        herror(hostname);
        exit(2);
    }
     
    //Start the port scan loop
    printf("Starting the portscan loop : \n");
    for( i = start ; i <= end ; i++) 
    {
        //Fill in the port number
        sa.sin_port = htons(i);
        //Create a socket of type internet
        sock = socket(AF_INET , SOCK_STREAM , 0);
         
        //Check whether socket created fine or not
        if(sock < 0) 
        {
            perror("\nSocket");
            exit(1);
        }
        //Connect using that socket and sockaddr structure
        err = connect(sock , (struct sockaddr*)&sa , sizeof sa);
         
        //not connected
        if( err < 0 )
        {
            //printf("%s %-5d %s\r" , hostname , i, strerror(errno));
            fflush(stdout);
        }
        //connected
        else
        {
            printf("%-5d open\n",  i);
        }
        close(sock);
    }
     
    printf("\r");
    fflush(stdout);
    return(0);
}

does it work??

is < and html encode error?
counldn't find where is it's definiation

Hi, when I try to compilate this code the compiler throw me an error. It's says:

use of undeclared identifier 'amp

Could you explain what is amp please??

Hi, when I try to compilate this code the compiler throw me an error. It's says:

use of undeclared identifier 'amp

Could you explain what is amp please??

i found the same code in a other website and it dated since 2013 so i think it doesnt work

Although I don't see the "amp" you're talking about. I believe this code is an attempt to correct the HTML encoding as seen here. https://www.binarytides.com/tcp-connect-port-scanner-c-code-linux-sockets/comment-page-1/?unapproved=243282&moderation-hash=b537728250f6e31ca1745b6518b20629#comment-243282

just delete "amp" and leave the "&" which is called an "amp"ersand.

Nice Bro