Justification

Re-declaration of identifiers results in confusing code, even if the identifiers belong to different name spaces. Using the same name may confuse the reader.

Example

int value;
/* ... */
{
    float value; /* WRONG: obscures earlier 'value' */
    /* ... */
}    
/* ... */

Note

The gcc compiler option "-Wshadow" is able to check this rule. This also accounts for an identifier declared as typedef.