cat <<EOF >arg.c
#include <stdio.h>
int main(int argc, char *argv[])
{
        printf("argv[1]=%s\n", argv[1]);
        return(0);
}
EOF

gcc arg.c -o arg

./arg "$(command which prints something)"

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

int main()
{
       char buf[512];
        FILE *fp=popen("ls", "r");
        while(fgets(buf, 512, fp)) printf("Got line '%s'\n", buf);

        pclose(fp);
}