Question

1) Write a C program that displays all the command line arguments that
   appear on the command line when the program is invoked. Use the
   file name cl.c for your c program. Test your program with

   cl hello goodbye
     and
   cl 1 2 3 4 5 6 7 8
     and
   cl

2) Write a C program which displays the sum of the command line
   arguments. Hint: use sscanf to convert the decimal arguments 
   (which are strings) to binary numbers that can be added. Use
   the file name sum.c for your program. Test your program with

   sum 5 -10 3
      and
   sum 8
      and
   sum

3) Write a C program that reads in a file and outputs it in
   reverse order. Use recursion. Test your program with the
   file reverse.txt (on our web site).  Hint: Structure of
   the recursive function reverse that you need:

      if not at end of file
          read line
          save line in a safe area (use strdup to do this)
          call reverse
          display line that was saved

   Use fgets to read line. Recall fgets returns 0 (which represents
   false) on end of file.

Answer 1

1.

// command line arguments
#include<stdio.h>

int main(int argc,char* argv[])
{
   int i;
   if(argc==1)
       printf("\nNo Extra Command Line Argument");
   if(argc>=2)
   {
       printf("\nNumber Of Arguments Passed: %d",argc); //Including file name
       printf("\nThe Command Line Arguments Passed are ");
       for(i=0;i<argc;i++)
           printf("\n %s",argv[i]);
   }
   printf("\n");
   return 0;
}

Output:

2.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc,char* argv[])
{
   int i,sum=0;
   int arr[argc-1];
   if(argc == 1)
       printf("\nNo numbers are entered");
   if(argc>=2)
   {
       for(i=0;i<argc;i++)
       {
           sscanf(argv[i],"%d",&arr[i-1]);
       }
       for(i=0;i<argc-1;i++)
           sum= sum + arr[i];
       printf("\nSum of the given numbers is %d",sum);
   }
   printf("\n");
}

Output:

3.

#include<stdio.h>
#include <string.h>

char* reverse(FILE *fp,char *str)
{
   char *p,*q,*res;
   if( fgets (str, 60, fp)!=NULL )
   {  
       q=strdup(str);
       reverse(fp,str);
       printf("%s",q);
   }
else
{
return "";
   }
   return str;
}

int main () {
FILE *fp;
char str[60];
char *res;

/* opening file for reading */
fp = fopen("file.txt" , "r");
res=reverse(fp,str);
fclose(fp);

return(0);
}

Output:

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