# V2584\. MISRA\. Expression used in condition should have essential Boolean type\.

This diagnostic rule is based on the [MISRA](https://www.misra.org.uk/) \(Motor Industry Software Reliability Association\) software development guide\.

This rule only applies to programs written in C\. Expressions used in 'if' / 'for' / 'while' conditions should have essential Boolean type\.

The MISRA standard introduces the essential type model, where a variable might have one of the following types:

* **Boolean**, if it uses true/false values: '\_Bool';
* **signed**, if it uses signed integer numbers, or is an unnamed enum: 'signed char', 'signed short', 'signed int', 'signed long', 'signed long long', 'enum \{ \.\.\.\. \};';
* **unsigned**, if it uses unsigned integer numbers: 'unsigned char', 'unsigned short', 'unsigned int', 'unsigned long', 'unsigned long long';
* **floating**, if it uses floating point numbers: 'float', 'double', 'long double';
* **character**, if it uses only characters: 'char';
* **Named enum**, if it uses a named set of user\-specific values: 'enum name \{ \.\.\.\. \};'

Thus, the standard allows the following expressions:

* expression of type bool \(from C99\);
* expression containing a comparison with '\=\=', '\!\=', '<', '\>', '<\=', '\>\=' operators;
* constants with value 0 or 1\.

An example for which the analyzer will issue a warning:

```cpp
void some_func(int run_it)
{
  if (run_it)
  {
    do_something();
  }

  // ....
}
```

Here the variable should be explicitly checked against zero:

```cpp
void some_func(int run_it)
{
  if (run_it != 0)
  {
    do_something();
  }

  // ....
}
```

Another example:

```cpp
void func(void *p)
{
  if (!p) return;
  // ....
}
```

To eliminate the issue, the pointer should be explicitly compared with the null:

```cpp
void func(void *p)
{
  if (p == NULL) return;
  // ....
}
```

The analyzer will not issue a warning for such code:

```cpp
void fun(void)
{
  while (1)
  {
    // ....
  }
}
```