Thread: CIN Input count question?

Hi,

I am doing a part time degree and need some help to finish off some code for my first assignment in C++. I have written a program which checks some inputted int's and strings, validates them and outputs the result. The last thing I need to do to finish my program below is to have my CIN command check to see if there are more than 5 items (3 int's and 2 strings) entered onto the single input line, and if so, output the an error "Invalid Input". I don't know how to use a loop or anything else to check if more than 5 items have been input on my cin line. For example, 2 + 2 = 4 is a valid input, but 2 + 2 = 3 + 1 should read as invalid. Here is my code:

Code:

#include <iostream>
#include <string>

using namespace std;

int main()
{
	int a = 0;
	int b = 0;
	int total = 0;

	string oper1, oper2;

	cout << "Please key in your equation." << endl;
	cin >> a >> oper1 >> b >> oper2 >> total;

	if (cin.fail())
		{
			cout << "Invalid input" << endl;
			exit(1);
		}

	else finished = true;


	if (oper1 == "+")
		{
			if (oper2 == "=")

				if (a + b == total)
					cout << "Correct" << endl;

				else cout << "Incorrect" << endl;

			else if (oper2 != "=")
				cout << "Invalid input" << endl;
		}

	else if (oper1 == "-")
		{
			if (oper2 == "=")

				if (a - b == total)
					cout << "Correct" << endl;

				else cout << "Incorrect" << endl;

			else if (oper2 != "=")
				cout << "Invalid input" << endl;
		}

	else if (oper1 != "+" || oper1 != "-")
		cout << "Invalid input" << endl;

	cout << endl << "a =  " << a << endl;
	cout << "oper1 =  " << oper1 << endl;
	cout << "b =  " << b << endl;
	cout << "oper2 =  " << oper2 << endl;
	cout << "total =  " << total << endl;
    cout << endl << "The equation you keyed in was: " << a << oper1 << b << oper2 << total << endl;
}

Any help appreciated.

Kam

It might be easier to use cin.getline(); and then parse the line after you read it. Using getline you would know it would read the entire line (up to any '\n' i think). It would read it in as an array of chars instead of a string but you could use something like this.

Code:

char input[201];
cin.getline(input, 200);
string str = new string(input);

then the string str would contain all the input and you could use all the features of c++ strings to extract the information. Like find and substr. I'm not sure if this is what you're looking. But it's a pretty easy way read in a whole line, that's why i thought it might help.

http://www.cplusplus.com/ref/iostrea...m/getline.html
http://www.cppreference.com/cppstring/index.html

"This same question (exactly) was asked recently."

Must have been someone else from my class on this forum!

Daved, you are a legend. I have been trying various things for the past few days, and I new there was a way, but with my limited knowledge didn't know what. There had to be a better, more efficient way to do this rather than using a string input for the equation line and breaking that down and doing int conversions etc.

Just to clarify if I understand this correctly, cin.get() reads the next character from the stdin, in my case, for eg. if 2 + 5 = 7 + 4 was input. In my program, there are only enough variables to read up to 7, so cin.get() would then contain + from the buffer, not a \n.

Here is the code I included to my program below the if (cin.fail()) statement to make it work.

Code:

else if (cin.get() != '\n')
		{
			cout << "Invalid input" << endl;
			exit(1);
		}

Thanks for all your help guys, I will definetly be using this forum more as my course progresses!

Kam

Technically, cin.get() would grab the space ' ' from after the 7. The get() function is unformatted, so it does not skip whitespace like operator>>. If the user input "2 + 5 = 7 " (note the space at the end) then your code would print "Invalid input". I would assume that is ok.

Yep, that is absolutely OK. Glad I understand how that works now. Many thanks again.

Kam