Variable not initialized in C++ code? - c++

Question

Edit: Thank you all very much for your answers, I know now that this was a stupid question, but I've been attempting to get into C++ after just getting a handle on Visual Basic, so a lot of these things I am unfamiliar with. I promise I'm not just asking them to waste your time.
I've been trying to do a sample project in C++ to learn the basics, and I'm having an issue with the current code. The program is supposed to add up user inputted variables and take into account which month they have entered to apply different charges. However, It says that my variable, usageCost, hasn't been initialized. Here's the code:
#include <iostream>
using namespace std;
int main()
{
string monthtext;
double month,
days,
hours,
kwhr,
completeCharge,
energyadjustCharge;
const double flatservicecharge = 5.31;
cout << "Enter the month (1-12) :";
cin >> month;
cout << "Number of days in the period :";
cin >> days;
cout << "Kilowatt hours used :";
cin >> hours;
if (month = 1){
monthtext = "January";
}
else{
if (month = 2){
monthtext = "February";
}
else{
if (month = 3){
monthtext = "March";
}
else{
if (month = 4){
monthtext = "April";
}
else{
if (month = 5){
monthtext = "May";
}
else{
if (month = 6){
monthtext = "June";
}
else{
if (month = 7){
monthtext = "July";
}
else{
if (month = 8){
monthtext = "August";
}
else{
if (month = 9){
monthtext = "September";
}
else{
if (month = 10){
monthtext = "October";
}
else{
if (month = 11){
monthtext = "November";
}
else{
if (month = 12){
monthtext = "December";
}
}
}
}
}
}
}
}
}
}
}
}
double usageCost;
if (month <= 5 && month >= 10 && hours <= 500){
usageCost = hours * 12.9266;
}
if (month <= 5 && month >= 10 && hours > 500){
usageCost = 500 * 12.9266 + (hours - 500) * 10.9917;
}
if (month >= 6 && month <= 9 && hours <= 750){
usageCost = 750 * 12.9266;
}
if (month >= 6 && month <= 9 && hours > 750){
usageCost = 750 * 12.9266 + (hours - 750) * 14.2592;
}
energyadjustCharge = hours * .1305;
completeCharge = usageCost + flatservicecharge + energyadjustCharge;
cin.get();
return 1;
}

Answer 1

You declare:
double usageCost;
but as you can see, you don't set it to any value, thus it is unintialized.
Compiler is correct.
Solution:
Try:
double usageCost = 0.0;
Edit 1:
Other Issues with your program:
Assignment uses "=", comparison uses "=="
Please change all your if statements accordingly.
Replace if statements with array lookup
Adding the following will simplify your program:
const std::string month_names[] =
{"No month index 0",
"January", "February", "March", "April",
"May", "June", "July", "August",
"September", "October", "November", "December"
};
// ...
month_text = month_names[month];

Answer 2

The error is because you have some code paths that never set usageCost. Rather than hide the error by initializing usageCost, it is better to fix your code which surely did intend to give usageCost a value in all cases.
In fact it is good that you didn't initialize usageCost because it meant you got a compiler warning to alert you to the later logic error.
month <= 5 && month >= 10 is never true. No month is before June and also after September. You probably meant (month <= 5 || month >= 10). The brackets are important because you have another && condition following.
However it would be better to avoid code duplication and avoid the possibility of none of the four cases being entered by rewriting that section:
if ( month >= 6 && month <= 9 )
{
if ( hours > 750 )
usageCost = ......;
else
usageCost = ......;
}
else
{
if ( hours > 500 )
usageCost = ......;
else
usageCost = ......;
}
With this structure it is impossible for usageCost to not be assigned something.

Answer 3

You have defined month to be a double.
double month;
cout << "Enter the month (1-12) :";
cin >> month;
If I type 5.5 for this input, you can see that usageCost will never be initialized to any value.
double usageCost;
// This will evaluate to false
if (month <= 5 && month >= 10 && hours <= 500){
usageCost = hours * 12.9266;
}
// This will evaluate to false
if (month <= 5 && month >= 10 && hours > 500){
usageCost = 500 * 12.9266 + (hours - 500) * 10.9917;
}
// This will evaluate to false
if (month >= 6 && month <= 9 && hours <= 750){
usageCost = 750 * 12.9266;
}
// This will evaluate to false
if (month >= 6 && month <= 9 && hours > 750){
usageCost = 750 * 12.9266 + (hours - 750) * 14.2592;
}
Consider:
Initializing usageCost to a default value
using an int or similar for values that will only ever be "whole numbers".
using month > 5 as the true inverse of month <= 5

Answer 4

I fixed a number of issues for you.
#include <iostream>
using namespace std;
int main()
{
string monthtext;
double month,
days,
hours,
kwhr,
completeCharge,
energyadjustCharge;
const double flatservicecharge = 5.31;
cout << "Enter the month (1-12) :";
cin >> month;
cout << "Number of days in the period :";
cin >> days;
cout << "Kilowatt hours used :";
cin >> hours;
struct {int input; string month;} Calendar[] = {
{ 1, "January" },
{ 2, "February" },
{ 3, "March" },
{ 4, "April" },
{ 5, "May" },
{ 6, "June" },
{ 7, "July" },
{ 8, "August" },
{ 9, "September" },
{ 10, "October" },
{ 11, "November" },
{ 12, "December" } };
for(int i = 0; i < ARRAY_SIZE(Calendar); ++i)
{
if (month == Calendar[i].input)
{
monthtext = Calendar[i].month;
break;
}
}
double usageCost = 0.0;
if (month <= 5 && month >= 10 && hours <= 500)
{
usageCost = hours * 12.9266;
}
if (month <= 5 && month >= 10 && hours > 500)
{
usageCost = 500 * 12.9266 + (hours - 500) * 10.9917;
}
if (month >= 6 && month <= 9 && hours <= 750)
{
usageCost = 750 * 12.9266;
}
if (month >= 6 && month <= 9 && hours > 750)
{
usageCost = 750 * 12.9266 + (hours - 750) * 14.2592;
}
energyadjustCharge = hours * .1305;
completeCharge = usageCost + flatservicecharge + energyadjustCharge;
cin.get();
return 0;
}