Can please anyone explain this function?

Question

inline long long read()
{
long long ret=0,cc=gc();
long long f=0;
for(;(cc<'0'||cc>'9')&&cc!='-';)
cc=gc();
if(cc=='-'){f=1;cc=gc();}
for(;cc>='0'&&cc<='9';)
{
ret=ret*10+cc-'0';
cc=gc();
}
return f?-ret:ret;
}

Answer 1

a third party function is been called, which will be needed to explain the code