Why do my stream input operations get skipped over? - c++

Question

I have this code where in option lists will display when run. my problem is when I enter number 2, the option 2 program doesn't work well. It just go directly to asking the amount paid instead of asking first the cost of purchase.
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
float circle (float a)
{
float z;
z = 3.141593 * (a * a);
return (z);
}
float square (float b)
{
float y;
y = b * b;
return (y);
}
float rectangle (float c, float d)
{
float x;
x = c * d;
return (x);
}
float triangle (float e, float f)
{
float w;
w = (e * f) / 2;
return (w);
}
void exit ()
{
cout << "THANK YOU! GOODBYE!" << endl;
}
int main()
{
int x;
do
{
cout << "Please choose an option below: \n";
cout << "1. Area of Shapes\n";
cout << "2. Cost of your items\n";
cout << "3. Flood Control\n";
cout << "4. Fibonacci Numbers\n";
cout << "5. Addition Table\n";
cout << "6. Exit\n";
cin >> x;
if (x == 1)
{
system("cls");
float n;
float l;
float m;
float radius;
float side;
float length;
float width;
float base;
float height;
do
{
cout << "1 => Area of Circle" << endl;
cout << "2 => Area of Square" << endl;
cout << "3 => Area of Rectangle" << endl;
cout << "4 => Area of Trian1gle" << endl;
cout << "5 => Return to Main Menu" << endl;
cout << "0 => Exit" << endl;
cout << "Please enter number of your choice: ";
cin >> n;
system("cls");
{
if (n == 0)
{
exit ();
system("pause");
return 0;
}
else if (n == 1)
{
cout << "Enter radius of the circle: ";
cin >> radius;
l = circle (radius);
cout << "Area of the circle is: " << l << endl;
system("pause");
system("cls");
}
else if (n == 2)
{
cout << "Enter side of the square: ";
cin >> side;
cout << "Area of the square is: " << square (side) << endl;
system("pause");
system("cls");
}
else if (n == 3)
{
cout << "Enter length of the rectangle: ";
cin >> length;
cout << "Enter width of the rectangle: ";
cin >> width;
m = rectangle (length, width);
cout << "Area of the rectangle is: " << m << endl;
system("pause");
system("cls");
}
else if (n == 4)
{
cout << "Enter base of the triangle: ";
cin >> base;
cout << "Enter height of the triangle: ";
cin >> height;
cout << "Area of the triangle is: " << triangle (base, height) << endl;
system("pause");
system("cls");
}
else if (n == 5)
{
exit ();
}
else
cout << "Invalid number. Please enter a valid number below" << endl;
}
}
while (n != 0 && n != 5);
cout << endl << endl;
system("pause");
system("cls");
}
else if (x == 2)
{
system("cls");
string mystr;
float cost = 0;
float amount = 0;
float total;
cout << "Total Cost: P";
getline (cin, mystr);
stringstream(mystr) >> cost;
cout << endl;
total = cost * .06;
cout << "Sales Tax Value: P" << total << endl;
cout << endl;
cout << "Cost of Item: P" << cost + total << endl;
cout << endl;
cout << "Amount Paid: P";
getline (cin, mystr);
stringstream(mystr) >> amount;
cout << endl;
cout << "Total Amount Purchased: P" << cost << endl;
cout << "Sales Tax Value: P" << total << endl;
cout << "Total Amount + Sales Tax: P" << cost + total << endl;
cout << "Total Amount Paid: P" << amount << endl;
cout << "Change: P" << amount - (cost + total) << endl;
system("pause");
cout << endl;
cout << "THANK YOU! ENJOY YOUR MEAL!" << endl;
system("pause");
system("cls");
}
else if (x > 6)
cout << "Invalid Input";
else
{
system("pause");
return 0;
}
}
while (x != 6);
system("pause");
return 0;
}
EDIT
For the posters education
You do
switch (n) {
case 1:
//... Code for n == 1 - If long put into another function. If using local variables put code bloc in braces
break;
case 2:
// Diitto for n==2
default: // No match
// All other values of n not listed above
}

Answer 1

What went wrong
Say you type your menu selection:
2<Enter>
Then the content of the std::cin stream will be:
2\n
When your menu selection runs...
cin >> x;
...it reads a number off the line but doesn't consume any trailing whitespace nor the newline, so the remaining state content could be denoted like this:
\n
Then your code for menu option 2 starts running:
cout << "Total Cost: P";
getline (cin, mystr);
...the getline looks at std::cin and finds the left over \n mentioned above, and says "hey, an empty line - I'll set mystr to an empty string". Notice that it did not do what you'd hoped: namely wait for you to type some more input and read that into mystr.
How to fix it
Before calling getline(cin, mystr) you want to remove the left-over \n typed when entering the menu selection. The code changes for that (adding error handling too):
#include <limits>
...
cout << "Total Cost: P";
std::cin.ignore(std::numeric_limits<streamsize>::max(), '\n');
if (!std::getline(std::cin, mystr))
{
std::cerr << "unable to read mystr\n";
exit(1);
}
std::istringstream iss(mystr);
iss >> cost;
if (!iss)
{
std::cerr << "mystr doesn't contain a valid cost number\n";
exit(1);
}
How you could have found the problem
When you get stuck like this, try adding some "trace" statements to print out the values of variables and find where they differ from your expectation... that can at least give you a better idea how to isolate and describe the problem, and what to google for to fix it.
std::out << "mystr '" << mystr << "'\n";`
Try to use error handling like I've illustrated so the program stops (or prompts for better input) when there's a problem parsing the user's input.