Language: C

N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
#define Q(x)(x)*(x)
double D(i){return sqrt(Q(X[i]-cx)+Q(Y[i]-cy)+Q(Z[i]-cz));}
int L(){for(m=i=0;i<N;i++)if(D(i)>m)m=D(i),M=i;return M;}
main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
		for( i=0; i<N; ++i) scanf("%lf%lf%lf", X+i, Y+i, Z+i);
		cx = cy = cz = 0.5;
		for(d=0.5; d>1e-8; d/=2) {
			for(t=0; t<100; ++t) {
				int i = L();
				cx += (X[i]-cx)*d;
				cy += (Y[i]-cy)*d;
				cz += (Z[i]-cz)*d;
			}
		}
	}
exit(0);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'N' [-Wimplicit-int]
main.c:1:3: error: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
      |   ^
main.c:1:5: error: type defaults to 'int' in declaration of 'M' [-Wimplicit-int]
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
      |     ^
main.c: In function 'D':
main.c:3:8: error: type of 'i' defaults to 'int' [-Wimplicit-int]
    3 | double D(i){return sqrt(Q(X[i]-cx)+Q(Y[i]-cy)+Q(Z[i]-cz));}
      |        ^
main.c:3:20: error: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
    3 | double D(i){return sqrt(Q(X[i]-cx)+Q(Y[i]-cy)+Q(Z[i]-cz));}
      |                    ^~~~
main.c:1:1: note: include '<math.h>' or provide a declaration of 'sqrt'
  +++ |+#include <math.h>
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
main.c:3:20: warning: incompatible implicit declaration of built-in function 'sqrt' [-Wbuiltin-declaration-mismatch]
    3 | double D(i){return sqrt(Q(X[i]-cx)+Q(Y[i]-cy)+Q(Z[i]-cz));}
      |                    ^~~~
main.c:3:20: note: include '<math.h>' or provide a declaration of 'sqrt'
main.c: At top level:
main.c:5:1: error: return type defaults to 'int' [-Wimplicit-int]
    5 | main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
      | ^~~~
main.c: In function 'main':
main.c:5:1: error: type of 't' defaults to 'int' [-Wimplicit-int]
main.c:5:14: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    5 | main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
      |              ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
main.c:5:14: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    5 | main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
      |              ^~~~~
main.c:5:14: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:5:31: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    5 | main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
      |                               ^~~~~~
main.c:5:31: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:5:31: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:5:31: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:5:53: error: expected ')' before ';' token
    5 | main(t){for(;scanf("%d",&N),N;printf("%.f\n",D(L()));){
      |            ~                                        ^
      |                                                     )
main.c:17:1: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
   17 | exit(0);}
      | ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | N,i,M;double X[30],Y[30],Z[30],cx,cy,cz,d,m;
main.c:17:1: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
   17 | exit(0);}
      | ^~~~
main.c:17:1: note: include '<stdlib.h>' or provide a declaration of 'exit'