#include <stdlib.h>
を加えて、以下の修正を

typedef double REAL;
#define RANDM() (rand() / (double)RAND_MAX) /* uniform random deviates in (0,1) */
#define INITRAND() (srand(57731))

void buildtree(int k, int topvec[])
REAL length(void)
void optimize(REAL tol) /* a small positive number */
REAL error(void)
void output_tree(void)

int main(){ /* Inputs NUMSITES, DIMENSION, sites; outputs successive best Steiner
　　:
　　:
　　:
return 0;
} /* End of Steiner tree program. */