Language: C

i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
main.c:1:3: error: type defaults to 'int' in declaration of 'n' [-Wimplicit-int]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |   ^
main.c:1:30: error: return type defaults to 'int' [-Wimplicit-int]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                              ^
main.c: In function 'f':
main.c:1:30: error: type of 'x' defaults to 'int' [-Wimplicit-int]
main.c:1:30: error: type of 'y' defaults to 'int' [-Wimplicit-int]
main.c:1:112: error: implicit declaration of function 'strncmp' [-Wimplicit-function-declaration]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                ^~~~~~~
main.c:1:1: note: include '<string.h>' or provide a declaration of 'strncmp'
  +++ |+#include <string.h>
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
main.c:1:126: warning: 'strncmp' argument 3 type is 'int' where 'long unsigned int' is expected in a call to built-in function declared without prototype [-Wbuiltin-declaration-mismatch]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                              ^
<built-in>: note: built-in 'strncmp' declared here
main.c:1:136: error: implicit declaration of function 'puts' [-Wimplicit-function-declaration]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                        ^~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'puts'
  +++ |+#include <stdio.h>
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
main.c:1:144: error: implicit declaration of function 'exit' [-Wimplicit-function-declaration]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                ^~~~
main.c:1:1: note: include '<stdlib.h>' or provide a declaration of 'exit'
  +++ |+#include <stdlib.h>
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
main.c:1:144: warning: incompatible implicit declaration of built-in function 'exit' [-Wbuiltin-declaration-mismatch]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                ^~~~
main.c:1:144: note: include '<stdlib.h>' or provide a declaration of 'exit'
main.c: At top level:
main.c:1:154: error: return type defaults to 'int' [-Wimplicit-int]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                          ^~~~
main.c: In function 'main':
main.c:1:161: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                                 ^~~~~
main.c:1:161: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:161: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
main.c:1:161: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:181: error: implicit declaration of function 'strncat' [-Wimplicit-function-declaration]
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                                                     ^~~~~~~
main.c:1:181: note: include '<string.h>' or provide a declaration of 'strncat'
main.c:1:181: warning: incompatible implicit declaration of built-in function 'strncat' [-Wbuiltin-declaration-mismatch]
main.c:1:181: note: include '<string.h>' or provide a declaration of 'strncat'
main.c:1:216: error: 'W' undeclared (first use in this function)
    1 | i,n;char a[100002],s[999999];f(x,y){*a=x;a[1]=y;for(i=0;++i<=n;)a[i+1]=a[i]==87^a[i-1]==87^s[i]=='o'?83:87;if(!strncmp(a,a+n,2))a[n]=0,puts(a),exit(0);} main(){scanf("%d%s",&n,&s);strncat(s,s,n);f(83,83);f(83,87);f(W,83);f(W,W);puts("-1");}
      |                                                                                                                                                                                                                        ^
main.c:1:216: note: each undeclared identifier is reported only once for each function it appears in