c-gcc, 58 bytes

Result

AC

Duration

563ms

Code [DL]

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

stdin

FWOMOCOMJGAACVNSCCRLZMIQLY

stdout

GYRQTIVUSQLMPJCITUKFUIFOKY

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 c;main(i){for(;c=getchar()-10;)putchar((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;)putchar((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;)putchar((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;)putchar((c-55+i++)%26+65);}
 ^
/tmp/code.c:1:32: warning: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
 c;main(i){for(;c=getchar()-10;)putchar((c-55+i++)%26+65);}
                                ^~~~~~~

strace