#include <stdbool.h>
bool x = true;

Option 1:
#include <stdbool.h>
Option 2:
typedef enum { false, true } bool;
Option 3:
typedef int bool;
enum { false, true };
Option 4:
typedef int bool;
#define true 1
#define false 0
Explanation:
Option 1 will work only if you use C99 (or newer) and its the "standard way" to do it.
Choose this if possible
Options 2,3 and 4 will have practice the same identical behavior. #2 and #3 don't use
#defines though which in my opinion is better.

The C99 standard for C language supports bool variables.
Unlike C++, where no header file is needed to use bool,
a header file “stdbool.h” must be included to use bool in C.
If we save the below program as .c, it will not compile,
but if we save it as .cpp, it will work fine.
#include<stdbool.h>

int a = 4;
int b = 5;
bool result;
result = a < b; // true
result = a > b; // false
result = a <= 4; // a smaller or equal to 4 - true
result = b >= 6; // b bigger or equal to 6 - false
result = a == b; // a equal to b - false
result = a != b; // a is not equal to b - true
result = a > b || a < b; // Logical or - true
result = 3 < a && a < 6; // Logical and - true
result = !result; // Logical not - false