Language: C

i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}

Compiler output:
main.c:1:1: warning: data definition has no type or storage class
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      | ^
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,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |   ^
main.c:1:5: error: type defaults to 'int' in declaration of 't' [-Wimplicit-int]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |     ^
main.c:1:7: error: return type defaults to 'int' [-Wimplicit-int]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |       ^~~~
main.c: In function 'main':
main.c:1:7: error: type of 'm' defaults to 'int' [-Wimplicit-int]
main.c:1:20: error: implicit declaration of function 'scanf' [-Wimplicit-function-declaration]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                    ^~~~~
main.c:1:1: note: include '<stdio.h>' or provide a declaration of 'scanf'
  +++ |+#include <stdio.h>
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
main.c:1:20: warning: incompatible implicit declaration of built-in function 'scanf' [-Wbuiltin-declaration-mismatch]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                    ^~~~~
main.c:1:20: note: include '<stdio.h>' or provide a declaration of 'scanf'
main.c:1:42: error: implicit declaration of function 'printf' [-Wimplicit-function-declaration]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                                          ^~~~~~
main.c:1:42: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:42: warning: incompatible implicit declaration of built-in function 'printf' [-Wbuiltin-declaration-mismatch]
main.c:1:42: note: include '<stdio.h>' or provide a declaration of 'printf'
main.c:1:79: error: implicit declaration of function 'fmax' [-Wimplicit-function-declaration]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                                                                               ^~~~
main.c:1:1: note: include '<math.h>' or provide a declaration of 'fmax'
  +++ |+#include <math.h>
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
main.c:1:79: warning: incompatible implicit declaration of built-in function 'fmax' [-Wbuiltin-declaration-mismatch]
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                                                                               ^~~~
main.c:1:79: note: include '<math.h>' or provide a declaration of 'fmax'
main.c:1:79: error: too many arguments to function 'fmax'
main.c:1:78: error: lvalue required as left operand of assignment
    1 | i,n,t;main(m){for(;scanf("%d",&i),n|i;n||printf("%d\n",m))!n--?t=m=-9e5,n=i:m=fmax(t+=i,m,t*=t>0);}
      |                                                                              ^