Language: C

a=100;double x[a][a],y[a][a],r,z;
main(n,m,i,j,k){for(;scanf("%d%d",&n,&m),m;printf("%.2f\n",r)){
memset(x,0,sizeof(x));
for(i=0;i<n;i++)for(j=0;j<n;j++)scanf("%lf",y[i]+j);
for(j=0;j<n;j++)x[0][j]=1;
for(i=1;i<m;i++)for(j=0;j<n;j++)for(k=0;k<n;k++)if(x[i][j]<(z=x[i-1][k]*y[k][j]))x[i][j]=z;
for(r=j=0;j<n;j++)r=r<x[m-1][j]?x[m-1][j]:r;
}exit(0);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | a=100;double x[a][a],y[a][a],r,z;
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
main.c:1:14: error: variably modified 'x' at file scope
    1 | a=100;double x[a][a],y[a][a],r,z;
      |              ^
main.c:1:14: error: variably modified 'x' at file scope
main.c:1:22: error: variably modified 'y' at file scope
    1 | a=100;double x[a][a],y[a][a],r,z;
      |                      ^
main.c:1:22: error: variably modified 'y' at file scope
main.c:2:1: error: return type defaults to 'int' [-Wimplicit-int]
    2 | main(n,m,i,j,k){for(;scanf("%d%d",&n,&m),m;printf("%.2f\n",r)){
      | ^~~~
main.c: In function 'main':
main.c:2:1: error: type of 'n' defaults to 'int' [-Wimplicit-int]
main.c:2:1: error: type of 'm' defaults to 'int' [-Wimplicit-int]
main.c:2:1: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:2:1: error: type of 'j' defaults to 'int' [-Wimplicit-int]
main.c:2:1: error: type of 'k' defaults to 'int' [-Wimplicit-int]
main.c:2:22: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    2 | main(n,m,i,j,k){for(;scanf("%d%d",&n,&m),m;printf("%.2f\n",r)){
      |                      ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | a=100;double x[a][a],y[a][a],r,z;
main.c:2:22: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    2 | main(n,m,i,j,k){for(;scanf("%d%d",&n,&m),m;printf("%.2f\n",r)){
      |                      ^~~~~
main.c:2:22: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:2:44: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    2 | main(n,m,i,j,k){for(;scanf("%d%d",&n,&m),m;printf("%.2f\n",r)){
      |                                            ^~~~~~
main.c:2:44: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:2:44: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:2:44: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:3:1: error: implicit declaration of function 'memset' [-Wimplicit-function-declaration]
    3 | memset(x,0,sizeof(x));
      | ^~~~~~
main.c:1:1: note: include '<string.h>' or provide a declaration of 'memset'
  +++ |+#include <string.h>
    1 | a=100;double x[a][a],y[a][a],r,z;
main.c:3:1: warning: incompatible implicit declaration of built-in function 'memset' [-Wbuiltin-declaration-mismatch]
    3 | memset(x,0,sizeof(x));
      | ^~~~~~
main.c:3:1: note: include '<string.h>' or provide a declaration of 'memset'
main.c:8:2: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
    8 | }exit(0);}
      |  ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | a=100;double x[a][a],y[a][a],r,z;
main.c:8:2: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
    8 | }exit(0);}
      |  ^~~~
main.c:8:2: note: include '<stdlib.h>' or provide a declaration of 'exit'