Language: C++

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;
typedef Long Long ll;

int main()
{
    string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
    string a;
    cin >> a;
    rep(i, 7)
    {
        if (a == s[i])
        {
            cout << (7 - i) << endl;
        }
    }
    return 0;
}

Compiler output:
a.cc:8:19: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                   ^~~~~
a.cc:8:26: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                          ^~~~~
a.cc:8:33: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                 ^~~~~
a.cc:8:40: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                        ^~~~~
a.cc:8:47: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                               ^~~~~
a.cc:8:54: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                                      ^~~~~
a.cc:8:61: warning: multi-character character constant [-Wmultichar]
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                                             ^~~~~
a.cc:4:9: error: 'Long' does not name a type; did you mean 'long'?
    4 | typedef Long Long ll;
      |         ^~~~
      |         long
a.cc: In function 'int main()':
a.cc:8:19: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                   ^~~~~
a.cc:8:26: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                          ^~~~~
a.cc:8:33: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                 ^~~~~
a.cc:8:40: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                        ^~~~~
a.cc:8:47: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                               ^~~~~
a.cc:8:54: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                                      ^~~~~
a.cc:8:61: error: conversion from 'int' to non-scalar type 'std::string' {aka 'std::__cxx11::basic_string<char>'} requested
    8 |     string s[] = {'SUN', 'MON', 'TUE', 'WED', 'THU', 'FRI', 'SAT'};
      |                                                             ^~~~~