Homework & Coursework Questions

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
int main()
{
 pid_t pid;
 char *sh="Shell>";
 int i,pathindex=0, ret;
 char line[80];   // getting the user prompt
 char *paths[20]={"NULL"}; // 20 values path array
 char *currentpath, *path;  // current path to execute in   
 char *arg[]={NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL} ;
//////////////////////////////////////////////////////////////////////////////
 path=getenv("PATH");
 currentpath=strtok(path,":");
 while (currentpath!=NULL)
  {
   paths[pathindex]=currentpath; // filling the paths array
   currentpath=strtok(NULL,":"); // from enviroment variable
   pathindex++;   // PATH.
  }
 system("/usr/bin/clear");
 printf("\n\nShell Program (OS Course)\n");
 printf("-------------------------\n\n");
 while (1)
  { 
   printf("%s",sh);
   gets(line);
   arg[0]=strtok(line," ");      // getting command
   if (strcmp(line,"leave")==0) exit(0);
   for (i=1;i<10;i++) arg[i]=strtok(NULL," "); //getting command arguments
   pathindex=0;
   while (paths[pathindex]!=NULL)
   {
    if ((pid=fork())<0)
    {
     printf("Error: Couldn't fork\n");
     exit(1);
    }
    if (pid==0)
    {
    printf("trying to run %s in %s\n",arg[0],paths[pathindex]);
    ret=execv(paths[pathindex],arg);
     if (ret==-1) exit(1);
    }
    else { wait(); pathindex++; }
   }
  }
 return 0;
}