c-gcc, 66 bytes

Result

AC

Duration

580ms

Code [DL]

c;main(i){for(;~scanf("%c\n",&c);i++)printf("%c",(c-65+i)%26+65);}

stdin

XHTXRUEPHICMAMNZAPQBJTNFDR

stdout

YJWBWALXQSNYNACPRHJVEPKDCR

stderr

/tmp/code.c:1:1: warning: data definition has no type or storage class
 c;main(i){for(;~scanf("%c\n",&c);i++)printf("%c",(c-65+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(;~scanf("%c\n",&c);i++)printf("%c",(c-65+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:1:17: warning: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
 c;main(i){for(;~scanf("%c\n",&c);i++)printf("%c",(c-65+i)%26+65);}
                 ^~~~~
/tmp/code.c:1:17: warning: incompatible implicit declaration of built-in function 'scanf'
/tmp/code.c:1:17: note: include '<stdio.h>' or provide a declaration of 'scanf'
/tmp/code.c:1:25: warning: format '%c' expects argument of type 'char *', but argument 2 has type 'int *' [-Wformat=]
 c;main(i){for(;~scanf("%c\n",&c);i++)printf("%c",(c-65+i)%26+65);}
                         ^
/tmp/code.c:1:38: warning: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
 c;main(i){for(;~scanf("%c\n",&c);i++)printf("%c",(c-65+i)%26+65);}
                                      ^~~~~~
/tmp/code.c:1:38: warning: incompatible implicit declaration of built-in function 'printf'
/tmp/code.c:1:38: note: include '<stdio.h>' or provide a declaration of 'printf'

strace