A question about my calculator program.

[hector_ronado]

Hi, I was having problem with my program. It still have some error when I typed in 5.0 and it only showed up 5 or I typed some other words that wasn't digit and it will be a big error. Can someone tell me what should I do to fix this?
Here's my homework assignment:
Write a Program that models a simple calculator. Each data entry line should consist of a valid operator (from the list below), and the right-hand operand. Assume that the left-hand operand is the accumulated value in the calculator, with an initial value of 0.0.
Acceptable operators:
+ ..Add
- ..Subtract
* ..Multiply
/ ..Divide
^ ..Power (raise left operand to the power of the right operand)
q or = ..Quit
Your Calculator should display the accumulated value after each operation. A sample run might be:
+ 5.0
Result so far is 5.00
^ 2
Result so far is 25.00
/ 2.0
Result so far is 12.50
Q 0
The final result is 12.50
Include (define and call) at least THREE functions:


a function that displays instructions to the user.
a function do_next_op() that has 3 input parameters (the operator, the operand, and the current accumulated value), and returns the new value for the accumulated value. An alternative implementation may use 2 input parameters (operator and operand), and 1 input/output parameter (the accumulated value)
at least one other function - of your choice! Make sure that it does something useful.


Here's my program code:


#include <iostream>
#include <cmath>
using namespace std;

void instruction ();
float do_next_op ( float&, float&, char );

int main()
{

instruction(); // displays instruction
float total;
float newentry;
char op;

total = 0;
// initialisation

cin >> op;
while (op != 'Q' && op != 'q' && op != '=')
{
cin >> newentry;
do_next_op (total, newentry, op);
cin >> op;
}
cout << "the final result is " << total << endl;

system ("pause");
return 0;
}

void instruction()
{

}

float do_next_op ( float &total, float &newentry,char op)
{

switch (op)
{
case '+': total = total + newentry;
break;
case '-': total = total - newentry;
break;
case '*': total = total * newentry;
break;
case '/': total = total / newentry;
if (newentry == 0)
{
cout << "divide by zero is unexecutable" << endl;
}
break;
case '^': total = pow (total,newentry);
break;
default : cout << " Unacceptable Operator(" << op << ")" << endl;
}

cout << "result so far is " << total << endl;
cout << endl;

return (total);
}

[hector_ronado]

Can someone help me out?

[Sinkingships7]

Putting your code in between code tags would help us help you.

[hector_ronado]

I already put my code in code tag~~

[Sinkingships7]

My bit of testing showed that your program worked well to the specifications.

I'm guessing your "big error" problem is from when you try to store a string in a float variable? If so, you may want to ignore this since it doesn't seem to be a requirement for the assignment.

If you want to fix it anyway, read up on exceptions and clearing the input stream (cin).

[hector_ronado]

But when I typed in +5.0, it should display 5.00. And my program only showed up 5, here's the biggest error...XD So can you tell me what should I change?

[eightmillion]

You need to tell cout to show the the point for values that are whole numbers. Something like this:

cout << showpoint;
cout.precision(3); // default precision is 6, which would print 5.00000

[dwhitney67]

My bit of testing showed that your program worked well to the specifications.
...

You're kidding right? Did you try to perform a division using 0 as the denominator (ie. newentry)? Ok I'll concede that you only did a 'bit' of testing, but still, the bug in the code is quite obvious with a spot-check. You don't even need to run the code. Maybe zero cannot be represented exactly as 0.0000000?

[dwhitney67]

@ the OP

For a calculator application, you should consider treating the "Calculator" as an object. To do so, you declare/define it as a class that provides support for the various operations that you wish to perform.

For example:


#include <iostream>
#include <stdexcept>

class Calculator {
public:
Calculator(double value = 0) : myTotal(value) {}

double operator+(double value) {
return (myTotal += value);
}

double operator-(double value) {
return (myTotal -= value);
}

double operator*(double value) {
return (myTotal *= value);
}

double operator/(double value) {
if (value == 0) throw std::runtime_error("divisor cannot be zero!");

return (myTotal /= value);
}

friend std::ostream& operator<<(std::ostream& os, const Calculator& calc) {
os << calc.myTotal;
return os;
}

private:
double myTotal;
};

int main() {
Calculator calc;

calc + 5;
calc - 1;
calc * 7;
calc / 2;

std::cout << "calc = " << calc << std::endl;

try {
calc / 0;
}
catch (std::exception& e) {
std::cerr << "Test dividing by zero... " << e.what() << std::endl;
}
}

[Sinkingships7]

You're kidding right? Did you try to perform a division using 0 as the denominator (ie. newentry)? Ok I'll concede that you only did a 'bit' of testing, but still, the bug in the code is quite obvious with a spot-check. You don't even need to run the code. Maybe zero cannot be represented exactly as 0.0000000?

Yeah, I noticed that right away. I really did mean the parts about a "bit" and "to the specifications". It didn't say he needed to catch errors.

I'll admit my post was of little use, though. I was quite tired.