With the help of Excel App instance. we can execute a Macro in VB code.

EXcelAppInstance.Application.Run("MacroName")

Return Code in JCL can b obtained by the use of COND paramater...it is used to know the return codes of previous steps.

- Use a COBOL II CALL statement to invoke a subprogram. This method is transparent to CICS, which sees only the one load module. 

- EXEC LINK is similar to a call; it invokes a separate CICS program and ends with a RETURN to the invoking program

- EXEC XCTL which transfers control to another CICS program and does not get control 

back. 

COBOL II allows for static calls which are more efficient than the LINK instruction which establishes a new run-unit. 

A system call is a function.subroutine which interrupts the currently executing program and transfers control to the interrupt routine.The contents of the executing program are saved and after the interrupt routine finishes its function,control is transferred back to the executing program. If we talk in the context of Linux then System calls are called kernel mode.

Whereas API (Application Programming Interface) is a function or a set of functions, objects, protocols or data-structures for the support of application development for developers/programmers. It is actually a kind of function definition which specifies how to make available of a specific service of the system/OS to the other program/process or system. Read more at: https://www.queryhome.com/48442/os-what-is-difference-between-system-call-and-api

The main types of system calls are as follows:

Process Control: These types of system calls are used to control the processes. Some examples are end, abort, load, execute, create process, terminate process etc.

File Management: These types of system calls are used to manage files. Some examples are Create file, delete file, open, close, read, write etc.

Device Management: These types of system calls are used to manage devices. Some examples are Request device, release device, read, write, get device attributes etc.

Information Maintenance: These types of system calls are used to set system data and get process information. Some examples are time, OS parameters, id, time used etc.

Communications: These types of system calls are used to establish a connection. Some examples are send message, received messages, terminate etc

As against malloc(), calloc() needs two arguments, the number of elements  to be allocated and the size of each element. For example,

 p = (int *) calloc (10, sizeof (int));

would allocate space for a 10- integer array. Additionally, calloc() would also set each of this element with a value 0.

Thus the above call to calloc() is equivalent to:

p = (int *) malloc (10 * sizeof (int));

memset (p, 0, 10 * sizeof( int ));

Yes, using the realloc() function as shown below:

main()

{

        int *p;

        p = ( int *) malloc (20) ;

        t = p;

        t = (int *) realloc ( p, 40);

        if ( t == NULL )

        Printf (" Cannot reallocate, leaves previous allocated region unchanged ");

       else

       {

              if ( p ==t )

              ;  / * the array expanded at the same region */

             else

            { 

                 free ( p ); / * deallocate the original array */

                 p = t;  /* set p to newly allocated region */

             }

      }

}  

#include "alloc.h"

#define MAXROW 3

#define MAXcol 4

main()

{

        int *p, i, J;

        p = (int *) malloc (MAXROW * MAXCOL * sizeof (int));

         for ( i=0; i < MaxROW ; i++)

         {

                for (j=0; j < MAXCOL ; j++)

                { 

                      p [ i * MAXCOL + j] = i;

                       printf ( "%d", p [i * MAXCOL + j] );

                 }

                  printf ("\n");

          }

}