Language: C++

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,m;
    string f,g;
    char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
    cin>>f>>g;
    if(f=="0")
    {
        n=0;
    }
    if(f=="1")
    {
        n=1;
    }
    if(f=="2")
    {
        n=2;
    }
    if(f=="3")
    {
        n=3;
    }
    if(f=="4")
    {
        n=4;
    }
    if(f=="5")
    {
        n=5;
    }
    if(f=="6")
    {
        n=7;
    }
    if(f=="8")
    {
        n=8;
    }
    if(f=="9")
    {
        n=9;
    }
    if(f=="A")
    {
        n=10;
    }

    if(f=="B")
    {
        n=11;
    }
    if(f=="C")
    {
        n=12;
    }
     if(f=="D")
    {
        n=13;
    }
     if(f=="E")
    {
        n=14;
    }
     if(f=="F")
    {
        n=15;
    }
    if(g=="1")
    {
        m=1;
    }
    if(g=="2")
    {
        m=2;
    }
    if(g=="3")
    {
        m=3;
    }
    if(g=="4")
    {
        m=4;
    }
    if(g=="5")
    {
        m=5;
    }
    if(g=="6")
    {
        m=6;
    }
    if(g=="7")
    {
        m=7;
    }
    if(g=="8")
    {
        m=8;
    }
    if(g=="9")
    {
        m=9;
    }
    if(g=="A")
    {
        m=10;
    }
    if(g=="B")
    {
        m=11;
    }
    if(g=="C")
    {
        m=12;
    }
    if(g=="D")
    {
        m=13;
    }
    if(g=="E")
    {
        m=14;
    }
    if(g=="F")
    {
        m=15;
    }
    if(g=="0")
    {
        m=0;
    }
        if(n>m)
        {
            cout<<">"<<endl;
            cout<<k[n]<<">"<<k[m]<<endl;
        }
        if(n<m)
        {
            cout<<"<"<<endl;
            cout<<k[n]<<"<"<<k[m]<<endl;
        }
         if(n==m)
        {
            cout<<"="<<endl;
            cout<<k[n]<<"="<<k[m]<<endl;
        }


}


Compiler output:
a.cc:7:57: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                         ^~~~
a.cc:7:62: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                              ^~~~
a.cc:7:67: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                   ^~~~
a.cc:7:72: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                        ^~~~
a.cc:7:77: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                             ^~~~
a.cc:7:82: warning: multi-character character constant [-Wmultichar]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                                  ^~~~
a.cc: In function 'int main()':
a.cc:7:57: error: narrowing conversion of '12592' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                         ^~~~
a.cc:7:62: error: narrowing conversion of '12593' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                              ^~~~
a.cc:7:67: error: narrowing conversion of '12594' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                   ^~~~
a.cc:7:72: error: narrowing conversion of '12595' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                        ^~~~
a.cc:7:77: error: narrowing conversion of '12596' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                             ^~~~
a.cc:7:82: error: narrowing conversion of '12597' from 'int' to 'char' [-Wnarrowing]
    7 |     char k[16]={'0','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15'};
      |                                                                                  ^~~~