which compiler to select???

which compiler shall i choose to upload my code ???
void main()

double n;
int i;


We don’t call it compiler.
Code chef have many programming questions and if you want to submit and check whether your code is correct solution to the problem then there is a “submit” button on top of page right hand side. click it. there you would see the editor. just paste your code there .At bottom of page select your language (which i guess is c++) and click another submit button below it.
Soon your result will be displayed whether answer is correct or not.

If you just want to compile any random code , code chef is not the place . use ideone .It’s quite famous and support many languages including c,c++,java.

If you want some software to compile your code , use codeblocks(for c and c++).
Hope that helps.