There are a few things wrong.

You aren't declaring main() to return an int, although the compiler is probably taking care of this for you.

main() is not returning a value.

rt is not the simple integer exit status that you think it is. rt contains other information regarding how the process exited (for example, if by a signal, which sig). You need to read the waitpid() man page for the details (which include macros to extract the actual exit status from system's return value).

system
wait

You omitted the stdlib.h include for system() and the wait-related macros required to work with its return value.

Code:

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

int
main(int argc, char *argv[])
{
    char *cmd=argv[1];
    int rt=system(cmd);
    if (WIFEXITED(rt)) {
        rt=WEXITSTATUS(rt);
        printf ("\n executed command: %s\n RETURN: %d\n", cmd, rt);
    }
    else
        rt=128;
    return rt;
}

Sample run:

Code:

$ ./a.out 'perl -e "exit 5"'; echo $?

 executed command: perl -e "exit 5"
 RETURN: 5
5

Regards,
Alister