Why is this an issue?

Excessive use of nested IF, ELSEIF, or ELSE statements increases cyclomatic complexity and degrades performance. Using a SWITCH statement or refactoring the code reduces CPU overhead and improves readability.

Functional rules

one variable must be used maximum twice in IF / ELSEIF / ELSE statements at the same level - WARNINGs :
IF and ELSEIF statements use explicitly variable names !
ELSE statements use implicity variable names !
one variable must be used maximum twice in IF / ELSEIF / ELSE statements at differents hierarchical levels
we can assume that if one variable is used three times or more, we should :
use a SWITCH statement instead
or refactor the code if possible

Examples

Noncompliant

NON compliant, because nb is used 4 times : - 2 explicit times in IF statements - 2 implicit times in ELSE statements

int index = 1;
int nb = 2;
...
if (nb == 0) {
    nb = index;
} else if (nb == 1) {
    nb = index * 2;
} else if (nb == 2) {
    nb = index * 3;
} else {
    nb = -1;
}
return nb;

Compliant

SWITCH statement solution + refactor solution

int index = 1;
int nb = 2;
...
switch (nb) {
    case 0:
    case 1:
    case 2:
        nb = index * (nb + 1);
        break;
    default:
        nb = -1;
}
return nb;