Language: C++

#include <iostream>
#include <cstdio>
#include <cmath>

int main() {
double a, b, c;
char op;

do{
std::cin >> a >> op >> b;

if(op == '+'){
c = floor(a + b);
printf('%.0f', c)
}
else if(op == '-'){
c = floor(a - b);
printf('%.0f', c)
}
else if(op == '*'){
c = floor(a * b);
printf('%.0f', c)
}
else if(op == '/'){
c = floor(a / b);
printf('%.0f', c)
}
else{
}
} while(!(op == '?'));
}

Compiler output:
a.cc:14:8: warning: multi-character character constant [-Wmultichar]
   14 | printf('%.0f', c)
      |        ^~~~~~
a.cc:18:8: warning: multi-character character constant [-Wmultichar]
   18 | printf('%.0f', c)
      |        ^~~~~~
a.cc:22:8: warning: multi-character character constant [-Wmultichar]
   22 | printf('%.0f', c)
      |        ^~~~~~
a.cc:26:8: warning: multi-character character constant [-Wmultichar]
   26 | printf('%.0f', c)
      |        ^~~~~~
a.cc: In function 'int main()':
a.cc:14:8: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
   14 | printf('%.0f', c)
      |        ^~~~~~
      |        |
      |        int
In file included from /usr/include/c++/14/cstdio:42,
                 from /usr/include/c++/14/ext/string_conversions.h:45,
                 from /usr/include/c++/14/bits/basic_string.h:4154,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 from a.cc:1:
/usr/include/stdio.h:363:43: note:   initializing argument 1 of 'int printf(const char*, ...)'
  363 | extern int printf (const char *__restrict __format, ...);
      |                    ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
a.cc:14:18: error: expected ';' before '}' token
   14 | printf('%.0f', c)
      |                  ^
      |                  ;
   15 | }
      | ~                 
a.cc:18:8: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
   18 | printf('%.0f', c)
      |        ^~~~~~
      |        |
      |        int
/usr/include/stdio.h:363:43: note:   initializing argument 1 of 'int printf(const char*, ...)'
  363 | extern int printf (const char *__restrict __format, ...);
      |                    ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
a.cc:18:18: error: expected ';' before '}' token
   18 | printf('%.0f', c)
      |                  ^
      |                  ;
   19 | }
      | ~                 
a.cc:22:8: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
   22 | printf('%.0f', c)
      |        ^~~~~~
      |        |
      |        int
/usr/include/stdio.h:363:43: note:   initializing argument 1 of 'int printf(const char*, ...)'
  363 | extern int printf (const char *__restrict __format, ...);
      |                    ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
a.cc:22:18: error: expected ';' before '}' token
   22 | printf('%.0f', c)
      |                  ^
      |                  ;
   23 | }
      | ~                 
a.cc:26:8: error: invalid conversion from 'int' to 'const char*' [-fpermissive]
   26 | printf('%.0f', c)
      |        ^~~~~~
      |        |
      |        int
/usr/include/stdio.h:363:43: note:   initializing argument 1 of 'int printf(const char*, ...)'
  363 | extern int printf (const char *__restrict __format, ...);
      |                    ~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
a.cc:26:18: error: expected ';' before '}' token
   26 | printf('%.0f', c)
      |                  ^
      |                  ;
   27 | }
      | ~