c-gcc, 63 bytes

Result

AC

Duration

558ms

Code [DL]

c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}

stdin

HZTXWQKCQAKBQTTSDYKUKWWSCW

stdout

IBWBBWRKZKVNDHIIUQDOFSTQBW

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}
 ^
/tmp/code.c:1:1: warning: type defaults to 'int' in declaration of 'c' [-Wimplicit-int]
/tmp/code.c:1:3: warning: return type defaults to 'int' [-Wimplicit-int]
 c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}
   ^~~~
/tmp/code.c: In function 'main':
/tmp/code.c:1:3: warning: type of 'i' defaults to 'int' [-Wimplicit-int]
/tmp/code.c:1:18: warning: implicit declaration of function 'getchar' [-Wimplicit-function-declaration]
 c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}
                  ^~~~~~~
/tmp/code.c:1:1: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
 c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}
 ^
/tmp/code.c:1:32: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 c;main(i){for(;c=getchar()-10;)printf("%c",(c-55+i++)%26+65);}
                                ^~~~~~
/tmp/code.c:1:32: warning: incompatible implicit declaration of built-in function 'printf'
/tmp/code.c:1:32: note: include '<stdio.h>' or provide a declaration of 'printf'

strace