code falling through on an if statement [closed] - c++

Question

Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers.
This question was caused by a typo or a problem that can no longer be reproduced. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers.
Closed 9 years ago.
Improve this question
When I add the second if to test for car size M to calculateTotalCarCharge then try to test the condition of c, I'm getting an answer for m (77.28 & 167.44) when I really want (68.73 & 148.92), its almost like the code is somehow falling through to the next condition
Test conditions
Type - Days - Amount
C - 3 - 68.73
M - 3 - 77.28
C - 7 - 148.92
M - 7 - 167.44
#include <iostream> //for I/O
#include <iomanip> //for formatting output
#include <cmath> //for math
using namespace std;
//prototypes
char validateCarChoice();
void displayProgramDescription();
int validateNumEntry(string prompt);
double calculateTotalCarCharge (char carSize, int daysRented);
//global constants
const char COMPACT = 'C';
const char MID = 'M';
const char FULL = 'F';
const char SUV = 'S';
const double COMPACT_DAILY_CHARGE = 22.91;
const double MID_DAILY_CHARGE = 25.76;
const double FULL_DAILY_CHARGE = 28.87;
const double SUV_DAILY_CHARGE = 98.88;
// --------------------------------------------------------------------------
// Description:
// Input parameter:
// Returns:
// ---------------------------------------------------------------------------
int main()
{
//local constants
const string ENTER_DAYS_RENTED = "Enter the number of days rented: ";
const string ENTER_MILES_DRIVEN = "Enter number of miles driven: ";
//local variables
char userCarTypeChosen;
char carSize;
int daysRented;
double milesDriven;
double carCharge;
//call function to display program description
displayProgramDescription();
//calls function to validate the car choice input by user
userCarTypeChosen = validateCarChoice();
//if car type chosen is suv (S) then only prompt will be to enter days
//rented, if not prompt both days rented and miles driven.
if (userCarTypeChosen == 'S')
{
daysRented = validateNumEntry(ENTER_DAYS_RENTED);
}
else
{
daysRented = validateNumEntry(ENTER_DAYS_RENTED);
milesDriven = validateNumEntry(ENTER_MILES_DRIVEN);
}
carCharge = calculateTotalCarCharge(carSize, daysRented);
//to be removed
cout << carCharge;
return 0;
}
// --------------------------------------------------------------------------
// Description: displayProgramDescription - displays program description
// Input parameter: N/A
// Returns: N/A
// ---------------------------------------------------------------------------
void displayProgramDescription()
{
//local constant
const string PROGRAM_DESCRIPTION = "This program will calculate a car rental"
" bill for Rent2U.";
//displays program description
cout << PROGRAM_DESCRIPTION << endl;
}
// --------------------------------------------------------------------------
// Description: validateCarChoice - displays menu of car options and daily cost.
// Then error checks that a valid choice was given
// Input parameter: N/A
// Returns: letter of car chosen
// ---------------------------------------------------------------------------
char validateCarChoice ()
{
//local constants
const string ENTER_CAR_LETTER = "Enter letter for car size rented: ";
const string ERROR_CAR_INPUT = "Re-enter letter for car size rented: ";
//local variable
char carSize;
//displays car size options
cout << "Car sizes:" << endl << endl;
cout << setw(5) << "C - Compact size at $ 22.91 per day" << endl;
cout << setw(5) << "M - Mid size at $ 25.76 per day" << endl;
cout << setw(5) << "F - Full size at $ 28.76 per day" << endl;
cout << setw(5) << "S - SUV at $ 98.88 per day" << endl << endl;
//prompt for user input
cout << ENTER_CAR_LETTER;
cin >> carSize;
carSize = toupper(carSize);
//validation of car type chosen
while (carSize !='C' && carSize !='M' && carSize !='F' && carSize !='S')
{
cout << ERROR_CAR_INPUT;
cin >> carSize;
carSize = toupper(carSize);
}
return carSize;
}
// --------------------------------------------------------------------------
// Description: validateNumEntry - validates that the user entry is at least 1
// Input parameter: prompt- prompts user to enter number
// Returns: the user inputed number
// ---------------------------------------------------------------------------
int validateNumEntry (string prompt)
{
//local constant
const string ERROR = "Error - entry must be at least 1.";
//local variable
double num;
cout << prompt;
cin >> num;
while (num < 1)
{
cout << ERROR << endl;
cout << prompt;
cin >> num;
}
return num;
}
// --------------------------------------------------------------------------
// Description:
// Input parameter:
// Returns:
// ---------------------------------------------------------------------------
double calculateTotalCarCharge (char carSize, int daysRented)
{
//local constant
const int WEEK = 7;
const double LOWER_WEEK_RATE = 6.5;
//local variable
double totalCarCharge;
int wholeWeek;
int extraDays;
if (carSize = 'C')
{
if (daysRented < WEEK)
{
totalCarCharge = (COMPACT_DAILY_CHARGE * daysRented);
}
else
{
wholeWeek = (daysRented / WEEK);
extraDays = (daysRented % WEEK);
totalCarCharge = ((wholeWeek * LOWER_WEEK_RATE *
COMPACT_DAILY_CHARGE) + (extraDays * COMPACT_DAILY_CHARGE));
}
}
//once i add this if condition, if I try and test C I get the calculations
//for M
if (carSize = 'M')
{
if (daysRented < WEEK)
{
totalCarCharge = (MID_DAILY_CHARGE * daysRented);
}
else
{
wholeWeek = (daysRented / WEEK);
extraDays = (daysRented % WEEK);
totalCarCharge = ((wholeWeek * LOWER_WEEK_RATE * MID_DAILY_CHARGE)
+ (extraDays * MID_DAILY_CHARGE));
}
}
return totalCarCharge;
}

Answer 1

For checking condition you have to use:
if (carSize == 'M')
and
if (carSize == 'C').
Because when you use the statement:
if (carSize = 'M') will just assign value carSize to 'M'
and will execute code inside the if statement.
This condition is same for if (carSize = 'C') too.
OR use switch statement:
switch (carSize)
{
case 'C':
if (daysRented < WEEK)
...
break;
case 'M':
// ...
}

Answer 2

As pointed out in the comments, you are assigning in your if statement in (carSize = 'C') and (carSize = 'M'). Out of interest, why not opt for a switch on the char here? It seems the branches are mutually exclusive, and you aren't mutating carSize in the branches? This might help avoid this kind issue in future:
switch (carSize)
{
case 'C':
if (daysRented < WEEK)
...
break;
case 'M':
// ...
}
Edit
There is a second bug in your code, in that you are assigning:
userCarTypeChosen = validateCarChoice();
But then you are passing the uninitialized variable carSize to the calculateTotalCarCharge function:
carCharge = calculateTotalCarCharge(carSize, daysRented);
You should change the assignment to carSize
carSize = validateCarChoice();
and then remove the userCarTypeChosen variable entirely.

Answer 3

In these comparisons to literals, a good idea can be to reverse the operands, which will throw a compiler error if you use single equal instead of double equal.
if (var == 'C') // compiles, runs correctly
if (var = 'C') // compiles, runs incorrectly, results in stackoverflow question
if ('C' == var) // compiles, runs correctly
if ('C' = var) // does not compile, fix this problem immediately