Gap

input/code.cpp: In function 'll FindGap(ll, ll)':
input/code.cpp:8:27: error: 'n' was not declared in this scope
         for (int i=1; i<=(n+1)/2; ++i){
                           ^
input/code.cpp:9:27: error: 'mn' was not declared in this scope
             MinMax(c, d, &mn, &mx);
                           ^~
input/code.cpp:9:27: note: suggested alternative: 'yn'
             MinMax(c, d, &mn, &mx);
                           ^~
                           yn
input/code.cpp:9:32: error: 'mx' was not declared in this scope
             MinMax(c, d, &mn, &mx);
                                ^~
input/code.cpp:15:25: error: 'n' was not declared in this scope
         for (int i=1; i<n; ++i){
                         ^
input/code.cpp:21:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^

#include <bits/stdc++.h>
#include "gap.h"
using namespace std;
typedef long long ll;
ll FindGap(ll a, ll b){
    if (a==1){
        ll c=0, d=1e18, t[100001], s=0;
        for (int i=1; i<=(n+1)/2; ++i){
            MinMax(c, d, &mn, &mx);
            t[i]=mn;
            t[n+1-i]=mx;
            c=mn-1;
            d=mx-1;
        }
        for (int i=1; i<n; ++i){
            c=t[i+1]-t[i];
            if (c>s) s=c;
        }
        return s;
    }
}