Language: C++

#include <iostream>
using namespace std;
int a[26];
int main() {
    string a;
    int i;
    bool flag=true;
    cin>>a;
    for(i=0;i<a.size();i++)
    {
    	switch(a[i])
    	case a: a[0]++; break; 
    	case b: a[1]++; break;
    	case c: a[2]++; break;
    	case d: a[3]++; break;
    	case e: a[4]++; break;
    	case f: a[5]++; break;
    	case g: a[6]++; break;
    	case h: a[7]++; break;
    	case i: a[8]++; break;
    	case j: a[9]++; break;
    	case k: a[10]++; break;
    	case l: a[11]++; break;
    	case m: a[12]++; break;
    	case n: a[13]++; break;
    	case o: a[14]++; break;
    	case p: a[15]++; break;
    	case q: a[16]++; break;
    	case r: a[17]++; break;
    	case s: a[18]++; break;
    	case t: a[19]++; break;
    	case u: a[20]++; break;
    	case v: a[21]++; break;
    	case w: a[22]++; break;
    	case x: a[23]++; break;
    	case y: a[24]++; break;
    	case z: a[25]++; break;
	}
	for(i=0;i<=25;i++)
	{
		if(a[i]%2!=0) flag=false;
	}
	if(flag==true) cout<<"Yes";
	else cout<<"No";
    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:12:14: error: the value of 'a' is not usable in a constant expression
   12 |         case a: a[0]++; break;
      |              ^
a.cc:5:12: note: 'a' was not declared 'constexpr'
    5 |     string a;
      |            ^
a.cc:12:14: error: could not convert 'a' from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'int'
   12 |         case a: a[0]++; break;
      |              ^
      |              |
      |              std::string {aka std::__cxx11::basic_string<char>}
a.cc:13:14: error: 'b' was not declared in this scope
   13 |         case b: a[1]++; break;
      |              ^
a.cc:13:9: error: case label '<expression error>' not within a switch statement
   13 |         case b: a[1]++; break;
      |         ^~~~
a.cc:14:14: error: 'c' was not declared in this scope
   14 |         case c: a[2]++; break;
      |              ^
a.cc:14:9: error: case label '<expression error>' not within a switch statement
   14 |         case c: a[2]++; break;
      |         ^~~~
a.cc:15:14: error: 'd' was not declared in this scope
   15 |         case d: a[3]++; break;
      |              ^
a.cc:15:9: error: case label '<expression error>' not within a switch statement
   15 |         case d: a[3]++; break;
      |         ^~~~
a.cc:16:14: error: 'e' was not declared in this scope
   16 |         case e: a[4]++; break;
      |              ^
a.cc:16:9: error: case label '<expression error>' not within a switch statement
   16 |         case e: a[4]++; break;
      |         ^~~~
a.cc:17:14: error: 'f' was not declared in this scope
   17 |         case f: a[5]++; break;
      |              ^
a.cc:17:9: error: case label '<expression error>' not within a switch statement
   17 |         case f: a[5]++; break;
      |         ^~~~
a.cc:18:14: error: 'g' was not declared in this scope
   18 |         case g: a[6]++; break;
      |              ^
a.cc:18:9: error: case label '<expression error>' not within a switch statement
   18 |         case g: a[6]++; break;
      |         ^~~~
a.cc:19:14: error: 'h' was not declared in this scope
   19 |         case h: a[7]++; break;
      |              ^
a.cc:19:9: error: case label '<expression error>' not within a switch statement
   19 |         case h: a[7]++; break;
      |         ^~~~
a.cc:20:14: error: the value of 'i' is not usable in a constant expression
   20 |         case i: a[8]++; break;
      |              ^
a.cc:6:9: note: 'int i' is not const
    6 |     int i;
      |         ^
a.cc:20:9: error: case label 'i' not within a switch statement
   20 |         case i: a[8]++; break;
      |         ^~~~
a.cc:21:14: error: 'j' was not declared in this scope
   21 |         case j: a[9]++; break;
      |              ^
a.cc:21:9: error: case label '<expression error>' not within a switch statement
   21 |         case j: a[9]++; break;
      |         ^~~~
a.cc:22:14: error: 'k' was not declared in this scope
   22 |         case k: a[10]++; break;
      |              ^
a.cc:22:9: error: case label '<expression error>' not within a switch statement
   22 |         case k: a[10]++; break;
      |         ^~~~
a.cc:23:14: error: 'l' was not declared in this scope
   23 |         case l: a[11]++; break;
      |              ^
a.cc:23:9: error: case label '<expression error>' not within a switch statement
   23 |         case l: a[11]++; break;
      |         ^~~~
a.cc:24:14: error: 'm' was not declared in this scope
   24 |         case m: a[12]++; break;
      |              ^
a.cc:24:9: error: case label '<expression error>' not within a switch statement
   24 |         case m: a[12]++; break;
      |         ^~~~
a.cc:25:14: error: 'n' was not declared in this scope
   25 |         case n: a[13]++; break;
      |              ^
a.cc:25:9: error: case label '<expression error>' not within a switch statement
   25 |         case n: a[13]++; break;
      |         ^~~~
a.cc:26:14: error: 'o' was not declared in this scope
   26 |         case o: a[14]++; break;
      |              ^
a.cc:26:9: error: case label '<expression error>' not within a switch statement
   26 |         case o: a[14]++; break;
      |         ^~~~
a.cc:27:14: error: 'p' was not declared in this scope
   27 |         case p: a[15]++; break;
      |              ^
a.cc:27:9: error: case label '<expression error>' not within a switch statement
   27 |         case p: a[15]++; break;
      |         ^~~~
a.cc:28:14: error: 'q' was not declared in this scope
   28 |         case q: a[16]++; break;
      |              ^
a.cc:28:9: error: case label '<expression error>' not within a switch statement
   28 |         case q: a[16]++; break;
      |         ^~~~
a.cc:29:14: error: 'r' was not declared in this scope
   29 |         case r: a[17]++; break;
      |              ^
a.cc:29:9: error: case label '<expression error>' not within a switch statement
   29 |         case r: a[17]++; break;
      |         ^~~~
a.cc:30:14: error: 's' was not declared in this scope
   30 |         case s: a[18]++; break;
      |              ^
a.cc:30:9: error: case label '<expression error>' not within a switch statement
   30 |         case s: a[18]++; break;
      |         ^~~~
a.cc:31:14: error: 't' was not declared in this scope
   31 |         case t: a[19]++; break;
      |              ^
a.cc:31:9: error: case label '<expression error>' not within a switch statement
   31 |         case t: a[19]++; break;
      |         ^~~~
a.cc:32:14: error: 'u' was not declared in this scope
   32 |         case u: a[20]++; break;
      |              ^
a.cc:32:9: error: case label '<expression error>' not within a switch statement
   32 |         case u: a[20]++; break;
      |         ^~~~
a.cc:33:14: error: 'v' was not declared in this scope
   33 |         case v: a[21]++; break;
      |              ^
a.cc:33:9: error: case label '<expression error>' not within a switch statement
   33 |         case v: a[21]++; break;
      |         ^~~~
a.cc:34:14: error: 'w' was not declared in this scope
   34 |         case w: a[22]++; break;
      |              ^
a.cc:34:9: error: case label '<expression error>' not within a switch statement
   34 |         case w: a[22]++; break;
      |         ^~~~
a.cc:35:14: error: 'x' was not declared in this scope
   35 |         case x: a[23]++; break;
      |              ^
a.cc:35:9: error: case label '<expression error>' not within a switch statement
   35 |         case x: a[23]++; break;
      |         ^~~~
a.cc:36:14: error: 'y' was not declared in this scope
   36 |         case y: a[24]++; break;
      |              ^
a.cc:36:9: error: case label '<expression error>' not within a switch statement
   36 |         case y: a[24]++; break;
      |         ^~~~
a.cc:37:14: error: 'z' was not declared in this scope
   37 |         case z: a[25]++; break;
      |              ^
a.cc:37:9: error: case label '<expression error>' not within a switch statement
   37 |         case z: a[25]++; break;
      |         ^~~~