I dont know if it's too late and you've already solved it, but chars in c are marked by single quotation marks: ''. Having: "" means you're trying to compare strings, which you must use strcmp for. str[j] is a char so your comparison should be with a char.

Please help me !!

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>

bool xo (const char* str)
{

int count = 0;
for (int i = 0; i < strlen(str); i++){
  if(str[i] == "x" || str[i] == "X"){
    count++;
  }
}

return count;

int countY = 0;
  for (int j = 0; j < strlen(str); j++;){
  if(str[j] == "y" || str[j] == "Y" ){
    countY++;
    }
}

return countY;

if (count == countY){
return true;
}
else {return false;}
}