I dont know how to cout for error

[diamondb]

I have an assignment which is to do a program that accepts only grades, in which I used float. but I dont how to add cout for invalid input. please help me. i really dont know how to do it. I been trying to figure it out for two days.

#include <iostream>
#include <stdlib.h>
#include <iomanip>

using namespace std;

int main(int argc, char** argv) {

float a=0, b=0, c=0, d=0, grade = 0;


cout << " Enter your Grade on Quiz no. 1 : \t";
cin >> a ;
cout << " Enter your Grade on Quiz no. 2 : \t";
cin >> b ;
cout << " Enter your Grade on Quiz no. 3 : \t";
cin >> c;
cout << " Enter your Grade on Quiz no. 4 : \t";
cin >> d;
system ("cls");

while ( a < -1 && b < -1 && c < -1 && d < -1 ) {
cout << " Enter your Grade on Quiz no. 1 : \t";
cin >> a ;
cout << " Enter your Grade on Quiz no. 2 : \t";
cin >> b ;
cout << " Enter your Grade on Quiz no. 3 : \t";
cin >> c;
cout << " Enter your Grade on Quiz no. 4 : \t";
cin >> d;
system ("cls");

if ( a > -1 && b > -1 && c > -1 && d > -1){
do{

cout << " Quiz#" << "\t\tGrade\n";
cout <<" 1\t\t" << a << endl;
cout <<" 2\t\t" << b << endl;
cout <<" 3\t\t" << c << endl;
cout <<" 4\t\t" << d << endl;
cout << "\n";

cout << " TOTAL AVE."<< "\t\tREMARKS\n";

grade = (a+b+c+d)/ 4;

if (grade> 94 && grade< 101 ) {

cout << " " << setw(4)<< left<<grade << "\t\tExcellent!\n\n";
}

else if (grade> 89 && grade< 95){

cout << " " << setw(4)<< left<< grade << "\t\tVery Satisfactory!\n\n";
}

else if (grade> 84 && grade< 90 ) {

cout << " " << setw(4)<< left<<grade << "\t\tSatisfactory!\n\n";
}

else if (grade> 79 && grade< 85 ) {

cout << " " << setw(4)<< left<<grade << "\t\tFine!\n\n";
}

else if (grade> 74 && grade< 80 ) {

cout << " " << setw(4)<< left<<grade << "\t\t\Fair!\n\n";
}

else if (grade> -1 && grade < 75 ) {

cout << " " << setw(4)<< left<<grade << "\t\t\Poor.\n\n";
}

else {
cout << " " << setw(4)<< left<< " " << "\t\t\Invalid Input.\n\n";
}
}
}

[shadowCODE]

#include <iostream>
using namespace std;

int main()
{
	int x;
	cout<<"Enter a value for x : ";
	cin>>x;

	//Use cin.fail() to check if input type matches variabe type
	//test by enetering a character for x.

	cin.fail() ? cout<<"Wrong input"<<endl : cout<<"Good to go!"<<endl;

	system("pause");
	return 0;
}

[giblit]

You can use !cin instead of cin.fail() as well. Easiest way would be simply to do
std::cout << (std::cin >> x ? "Good to go!" : "Wrong input") << std::endl;

[shadowCODE]

smooth..

[diamondb]

Thanks.. but I still dont get it.. I have variables that a,b,c,d that should be numbers only. thank you again

[shadowCODE]

What dont you understand?

[diamondb]

sorry.. the solutions that you provided are working.. it just that the program should repeat asking until the user give a correct input. it should only proceed to the next process if a valid input is given. thank you so much.. and sorry. I am really having a hard time here. I hope you will still help me.

[shadowCODE]

We provided you means of checking for correct input.

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

int main()
{
	int x;
	while(!(cin>>x))
	{
		cout<<"Wrong. Try again"<<endl;
		cin.clear();
		cin.ignore();
	}
	cout<<"Good to go"<<endl;
	system("pause");
	return 0;
}

[giblit]

You may want to ignore everything in the buffer and not just the last character. What if they enter asdfasdf instead of just a. Something like cin.ignore(1024, '\n'); or cin.ignore(numeric_limits<streamsize>::max(), '\n');

[diamondb]

you ideas are good. but after the first "while", it doesnt proceed to the next process. i dont know why

[Immo]

You have a few errors in your program with braces. You definitely need to get in the habit of using good bracing because that is what I believe was the cause of the problem here.

First, there is no closing brace to the while loop. On the line after system("cls"), you need to put a closing brace. Why? Think about it logically and you should be able to see why it makes no sense.

Secondly, you have what appears to be the beginning of a do-while loop. The do{ comes on the line after the large if-else statement, but it doesn't serve any purpose and you could do without it. Not only that, but it isn't even structured properly. Here's what that loop should look like:

do {
    // code
} while ( condition );

But like I said, you don't need it so just delete do{.

It should be able to compile safely after that.

EDIT: Also note that you don't need to do cin.fail() or cin.ignore() or anything like that. Just fix what I pointed out and it will run as you expected it to. Get in the habit of looking over everything line by line. Happy coding, mang. :-)