#include<stdlib.h>
#define USER "USER"
#define() VALUE "quantum6"
int main()
{
char* pEnv = getenv(USER);
if (pEnv)
{
printf(“%s=%s/n”, USER, pEnv);
}
setenv(USER, VALUE, 1);
printf("%s=%s\n", USER, getenv(USER));
unsetenv(USER);
printf("%s=%s\n", USER, getenv(USER));
}
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