gistfile1.c

int yearsToRetirementHelper(float principal, float rateOfReturn, float annualPostTaxIncome, float annualExpenses, int yearsToRetirementAcc) {
    float returnOnInvestment = principal * rateOfReturn;
    if (returnOnInvestment > annualExpenses) {
        return yearsToRetirementAcc;
    } else {
        float newStash = (principal + returnOnInvestment + annualPostTaxIncome) - annualExpenses;
        return yearsToRetirementHelper(newStash, rateOfReturn, annualPostTaxIncome, annualExpenses, yearsToRetirementAcc + 1);
    }
}

int yearsToRetirement(float principal, float rateOfReturn, float annualPostTaxIncome, float annualExpenses) {
    return yearsToRetirementHelper(principal, rateOfReturn, annualPostTaxIncome, annualExpenses, 0);
}