c-gcc, 86 bytes

Result

AC

Duration

1038ms

Code [DL]

h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}

stdin

61
20

stdout

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********************

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'h' [-Wimplicit-int]
/tmp/code.c:1:3: warning: data definition has no type or storage class
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
   ^
/tmp/code.c:1:3: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
/tmp/code.c:1:5: warning: data definition has no type or storage class
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
     ^
/tmp/code.c:1:5: warning: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
/tmp/code.c:1:7: warning: return type defaults to 'int' [-Wimplicit-int]
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
       ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:7: warning: type of 'w' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:19: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
                   ^~~~~
/tmp/code.c:1:19: warning: incompatible implicit declaration of built-in function 'scanf'
/tmp/code.c:1:19: note: include '<stdio.h>' or provide a declaration of 'scanf'
+#include <stdio.h>
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
                   ^~~~~
/tmp/code.c:1:41: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
                                         ^~~~~~~
/tmp/code.c:1:56: warning: '*' in boolean context, suggest '&&' instead [-Wint-in-bool-context]
 h;c;i;main(w){for(scanf("%d%d",&h,&w);h;putchar(++i%w/2*c?32:i>w?c=--h-1,i=0,10:42));}
                                                 ~~~~~~~^~