make, 134 bytes

Result

AC

Duration

1057ms

Code [DL]

a:
	@echo '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));}'|cc -xc -;echo $(STDIN:\n= )|./a.out

stdin

17
98

stdout

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

stderr

<stdin>:1:1: warning: data definition has no type or storage class
<stdin>:1:1: warning: type defaults to 'int' in declaration of 'h' [-Wimplicit-int]
<stdin>:1:3: warning: data definition has no type or storage class
<stdin>:1:3: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
<stdin>:1:5: warning: data definition has no type or storage class
<stdin>:1:5: warning: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
<stdin>:1:7: warning: return type defaults to 'int' [-Wimplicit-int]
<stdin>: In function 'main':
<stdin>:1:7: warning: type of 'w' defaults to 'int' [-Wimplicit-int]
<stdin>:1:19: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
<stdin>:1:19: warning: incompatible implicit declaration of built-in function 'scanf'
<stdin>:1:19: note: include '<stdio.h>' or provide a declaration of 'scanf'
<stdin>:1:41: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]