Language: C

char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}

Compiler output:
main.c:1:27: error: return type defaults to 'int' [-Wimplicit-int]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                           ^~~~
main.c: In function 'main':
main.c:1:27: error: type of 'c' defaults to 'int' [-Wimplicit-int]
main.c:1:40: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                        ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
main.c:1:40: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                        ^~~~~
main.c:1:40: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:64: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                                                ^~~~
main.c:1:64: note: include '<stdio.h>' or provide a declaration of 'puts'
main.c:1:110: error: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                                                                                              ^~~~~~~
main.c:1:110: note: include '<stdio.h>' or provide a declaration of 'putchar'
main.c:1:130: error: lvalue required as increment operand
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                                                                                                                  ^~
main.c:1:134: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                                                                                                                      ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
main.c:1:134: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
    1 | char r[99],g[99],*G,d[99];main(c){for(;scanf("%s%s%s",r,g,d)>1;puts(G))for(G=g,c=*G++,*g=0;*(G-1);)c=c-d[*g]?putchar(c),*G++:r[*g++];exit(0);}
      |                                                                                                                                      ^~~~
main.c:1:134: note: include '<stdlib.h>' or provide a declaration of 'exit'