• You have a complicated conditional (if-then-else) statement.
  Extract methods from the condition, then part, and else parts.
  

~cpp 
    if (data.before( SUMMER_START ) || data.after(SUMMER_END) )
        charge = quantity * _winterRate + _winterServeceCharge;
    else charge = quantity * _summerRate;

• You have a sequence of conditional tests with the same result.
  Combine them into a single conditional expression and extract it.
  

~cpp 
    double disabilityAmount() {
        if (_seniority < 2) return 0;
        if ( _monthsDisabled > 12) return 0;
        if ( _isPartTime) return 0;
        // compute the disability amount

~cpp 
    double disabilityAmount() {
        if( isNotEligableForDisability()) return 0;
        // compute the disability amount;

• The same fragment of code is in all branches of a conditional expression.
  Move it outside of the expression.
  

~cpp 
if (isSpecialDeal()){
    total = price * 0.95;
    send();
}
else {
    total = price * 0.98;
    send();
}

~cpp 
if (isSpecialDeal())
    total = price * 0.95
else     
    total = price * 0.98;
send();

• A method has conditional behavior that does not make clear the normal path of execution
  Use guard clauses for all the special cases.
  

~cpp 
double getPayAmount(){
    double result;
    if( _isDead) result = deadAmount();
    else {
        if (_isSeparated) result = separatedAmount();
        else {
            if (_isRetried) result = retiredAmount();
            else result = normalPayAmount();
        };
    }
    return result;

• You have a conditional that chooses different behavior depending on the type of and object
  Move each leg of the conditional to an overriding method in a subclass. Make the orginal method abstract.
  

~cpp 
    double getSpeed() {
        switch (_type) {
            case EUROPEAN:
                return getBaseSpeed();
            case AFRICAN:
                return getBaseSpeed() - getLoadFactor() * _numberofCoconuts;
            case NORWEGIAN_BLUE:
                return (_isNailed) ? 0 : getBaseSpeed(_voltage);
        }
        throw new RuntimeException ("Should be unreachable");
    }

• You have repeated checks for a null value
  Replace the null value with a null object.
  

~cpp 
    if (customer == null) plan = BillingPlan.basic();
    else plan = customer.getPlan();

~cpp 
          ┌───────┐
          │  Cutomer     │
          ├───────┤
          │getPlan       │
          └───────┘
                  △
                  │
          ┌───┴───┐
          │Null Customer │
          ├───────┤
          │getPlan       │
          └───────┘                

• A section of code assumes something about the state of the program.
  Make the assumption explicit with an assertion.
  

~cpp 
    double getExpenseLimit() {
        //should have eigher expense limit or a primary project
        return (_expenseLimit != NULL_EXPENSE)?
                _expenseLimit:
                _primaryProject.getMemberExpenseLimit();
    }

~cpp 
    double getExpenseLimit() {
        Assert.isTrue( _expenseLimit != NULL_EXPENSE || _primaryProject != null );
        return (_expenseLimit != NULL_EXPENSE)?
                _expenseLimit:
                _primaryProject.getMemberExpenseLimit();