Justification

Mixing relational and logical operators without explicitly adding parenthesis is a notorious source of error in C programs. However, care must be taken changing existing code which is not properly parenthesized.

The precedence of operators in C is not intuitive. Extra parentheses aid the reader to establish the grouping of operands.

Example 1

if (a == b && c == d && d != 0) /* WRONG */
{
   /* any statement */
}

Example 2

if ((a == b) && (c == d) && (d != 0)) /* RIGHT */
{
   /* any statement */
}

Example 3

if (i != 10) /* RIGHT: comparison of 1 value */
...

Example 4

if (i - k == 10 && j - k == 10) /* WRONG: precedence not clear  */
...

Example 5

if (((i - k) == 10) && ((j - k) == 10)) /* RIGHT */
...

Example 6

if (i <= 10) /* RIGHT: comparison of 1 value */
...

Example 7

if (i - k > 10 && j - k < 10) /* WRONG: precedence not clear */
...

Example 8

if (((i - k) > 10) && ((j - k) < 10)) /* RIGHT */
...

Note

Relational operators ("<=", "<", ">" and ">=") have a higher priority than the equality operators ("==" and "!="). Be careful with changing existing code which is not properly parenthesized!