Language: C

char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}

Compiler output:
main.c:1:24: error: return type defaults to 'int' [-Wimplicit-int]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                        ^~~~
main.c: In function 'main':
main.c:1:24: error: type of 'c' defaults to 'int' [-Wimplicit-int]
main.c:1:24: error: type of 'i' defaults to 'int' [-Wimplicit-int]
main.c:1:24: error: type of 'j' defaults to 'int' [-Wimplicit-int]
main.c:1:24: error: type of 'k' defaults to 'int' [-Wimplicit-int]
main.c:1:43: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}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],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
main.c:1:43: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                           ^~~~~
main.c:1:43: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:67: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                   ^~~~
main.c:1:67: note: include '<stdio.h>' or provide a declaration of 'puts'
main.c:1:102: error: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                                                      ^~~~~~
main.c:1:1: note: include '<string.h>' or provide a declaration of 'strlen'
  +++ |+#include <string.h>
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
main.c:1:102: warning: incompatible implicit declaration of built-in function 'strlen' [-Wbuiltin-declaration-mismatch]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                                                      ^~~~~~
main.c:1:102: note: include '<string.h>' or provide a declaration of 'strlen'
main.c:1:153: error: implicit declaration of function 'putchar' [-Wimplicit-function-declaration]
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                                                                                                         ^~~~~~~
main.c:1:153: note: include '<stdio.h>' or provide a declaration of 'putchar'
main.c: At top level:
main.c:1:180: error: expected declaration specifiers or '...' before numeric constant
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                                                                                                                                    ^
main.c:1:183: error: expected identifier or '(' before '}' token
    1 | char r[99],g[99],d[99];main(c,i,j,k){for(;scanf("%s%s%s",r,g,d)>2;puts(""))for(i=j=k=0,c=g[j++];i+j<=strlen(r)+strlen(g);){if(c==d[k])k++,c=r[i++];else putchar(c),c=g[j++];}}exit(0);}
      |                                                                                                                                                                                       ^