View Compilation Error

0_0_20488707_26410.cpp: In function 'int main()':
0_0_20488707_26410.cpp:17:7: error: 'x' was not declared in this scope
   for(x=0,sum=0,i=n;i>=1;i--){
       ^
0_0_20488707_26410.cpp:21:7: error: 'x' was not declared in this scope
   if(!x){
       ^
0_0_20488707_26410.cpp:26:14: error: 'x' was not declared in this scope
   for(i=1;i<=x;i++){//printf("%d %d\n",a[i].w+pre,a[i].l);
              ^