char *a;

void function()
{
    if(a == NULL)
    {
         a = "Test1";
    }
    else
    {
         a = "Test2";
    }
}

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

char *a;

void function();

int main( int argc, const char *argv[] )
{
    function();
    function();
    function();
    function();

    return 0;
}


void function()
{
    printf( "function: a=%s", (a ? a : "NULL") );

    if(a == NULL)
    {
         a = "Test1";
    }
    else
    {
         a = "Test2";
    }

    printf( "  exiting a=%sn", (a ? a : "NULL") );
}


This produces the following output:

function: a=NULL  exiting a=Test1
function: a=Test1  exiting a=Test2
function: a=Test2  exiting a=Test2
function: a=Test2  exiting a=Test2