Language: C

a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      | ^
main.c:1:1: error: type defaults to 'int' in declaration of 'a' [-Wimplicit-int]
main.c:1:3: error: type defaults to 'int' in declaration of 'i' [-Wimplicit-int]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |   ^
main.c:1:5: error: type defaults to 'int' in declaration of 'j' [-Wimplicit-int]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |     ^
main.c:1:7: warning: data definition has no type or storage class
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |       ^
main.c:1:7: error: type defaults to 'int' in declaration of 'u' [-Wimplicit-int]
main.c:1:14: error: type defaults to 'int' in declaration of 'd' [-Wimplicit-int]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |              ^
main.c:1:21: error: return type defaults to 'int' [-Wimplicit-int]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |                     ^~~~
main.c: In function 'main':
main.c:1:21: error: type of 'n' defaults to 'int' [-Wimplicit-int]
main.c:1:21: error: type of 's' defaults to 'int' [-Wimplicit-int]
main.c:1:31: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |                               ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
main.c:1:31: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |                               ^~~~~
main.c:1:31: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:84: error: 'm' undeclared (first use in this function)
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |                                                                                    ^
main.c:1:84: note: each undeclared identifier is reported only once for each function it appears in
main.c:1:169: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | a,i,j;u[101],d[101];main(n,s){scanf("%d",&n);for(;i<2;i++)for(j=0;j<n;)scanf("%d",&m[i][j++]);for(;--j>=0;){for(s=i=0;i<=j;)s+=u[i++];for(i--;i<n;)s+=d[i++];a=a<s?s:a;}printf("%d",a);}
      |                                                                                                                                                                         ^~~~~~
main.c:1:169: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:169: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:169: note: include '<stdio.h>' or provide a declaration of 'printf'