SRL Archive - C/C++ Help and Tutorials

hey guys okay so my program runs. Which is great.

But i need help with the bottom where it asks for the age.

What is the condition that i may have to set or if statement that detects a character.

For example say a user inter 'a' instead of an integer like '8'.

I want it to tell the user to enter a Integer.

How do i do that?

#include "StdAfx.h"
#include<iostream>
#include <cstdlib>
#include <string>
using namespace std;

int main()
{
    char ans; // The user's answer to the question
    int age; // The user's age
    bool correct = false; // The boolean flag

    ans = ' ';
    
    ////////////////////////////////
    // Beginning of your code
    
// Ask the user a yes/no question and make sure the response is
// either y or n

	while ( (ans != 'y') && (ans != 'n') ) 
{

		cout << " Do you want a college degree (y/n) ";
		cin >> ans;
		cout << endl;

			if ( (ans != 'y') && (ans != 'n') )

				cout << " Incorrect Value "
				    << endl
				 << endl;

}


	while (!correct)
{
	cout << " Enter your age as an integer: ";
	cin >> age;
	cout << endl;

		if ( !cin )
{
		
		cin.clear();
		cin.ignore(2000, '\n');
		
}
	else 

	correct = true;
	cout << "Thanks for your input!" << endl;
}

    system("pause");
    
    return 0;

}

You can use isdigit() to check if the first character is a digit, and then use atoi() to convert it to integer to be used as the age.

From: Frement
You can use isdigit() to check if the first character is a digit, and then use atoi() to convert it to integer to be used as the age.

not the answer im looking for.

From: Overtime
not the answer im looking for.

You can use isdigit() to check if the character is a digit or not, I gave you the answer you were looking for, and added some extra information :)

i want something i can use in an if statement.

if (isdigit(string_variable[0])) { //do something }

Something simple, im in a beginner class. My professor will be like wtf. Its something ive learned before, but forgot it.

How do i get it to only accept integers?

something like this. but i want it to be ANY character. Not just "M" or "F"

char gender = ‘ ‘; bool correct = false; 
while( !correct ) { 
// get user input for gender 
if( (gender != ‘M’) && (gender != ‘F’) ) { 
cout << &#8220;Incorrect value&#8221; << endl; 
} else { 
correct = true; 
}

Do you mean something like this:

if (age.fail()){

blah;
blah;
}

I think you could also do:

if (!age){

blah;
blah;
}

//Now if I type my gender as: Male, the program would accept it.
if (tolower(gender[0]) == "m" || tolower(gender[0]) == "f") {
	correct = true;
}

//And heres an example for your age problem.
int age_len = (sizeof(age) / sizeof(char));
for (int i = 0; i < age_len; i++) {
	if (!isdigit(age[i])) {
		correct = false;
		break;
	}
	if (i == age_len) {
		correct = true;
	}
}

Yea we aren't that advanced in our class yet. Im looking for something more basic.

From: Overtime
Yea we aren't that advanced in our class yet. Im looking for something more basic.

That is basic, I can't make it more basic for you :( At least I don't know how to.

Give this a go:

if (!(cin >> age))
	{
		
	cin.clear();
	cin.ignore(2000, '\n');
		
	}
        else
        { 

	correct = true;
	cout << "Thanks for your input!" << endl;
}

From: sf411
Give this a go:

if (!(cin >> age))
	{
		
	cin.clear();
	cin.ignore(2000, '\n');
		
	}
        else
        { 

	correct = true;
	cout << "Thanks for your input!" << endl;
}

^^ I don't think you fully understand what you are even typing :p. Checking to see if something gotten off of the stream (cin) and negating it will not tell you if what they entered is valid :duh:

http://www.cplusplus.com/reference/clibrary/cstdio/getchar/

getchar() possibly?

Then use the value returned and compare it to the ascii chart values for numerical values (numbers)? This is the method mosts of my beginner classes wanted for comparing/checking to see if things were of the correct format.

From: HyperSecret
^^ I don't think you fully understand what you are even typing :p. Checking to see if something gotten off of the stream (cin) and negating it will not tell you if what they entered is valid :duh:

http://www.cplusplus.com/reference/clibrary/cstdio/getchar/

getchar() possibly?

Then use the value returned and compare it to the ascii chart values for numerical values (numbers)? This is the method mosts of my beginner classes wanted for comparing/checking to see if things were of the correct format.

I do not think you know what you are talking about. I just tried it and it works.

From: sf411
Give this a go:

if (!(cin >> age))
	{
		
	cin.clear();
	cin.ignore(2000, '\n');
		
	}
        else
        { 

	correct = true;
	cout << "Thanks for your input!" << endl;
}

Thats actually very clever, I would never have thought of that :) But doesn't seem to be beginner stuff :D

As aforementioned, isdigit is the most simplest possible way and is of beginner level.

Use it. You won't get marked down for doing your own research. Google "c++ check if cin is number" and check the results. :)

	while (!correct)
{
	cout << " Enter your age as an integer: ";
	cin >> age;
	cout << endl;

		if (!cin.good())
		{
		cout << " Enter a Integer."
			<< endl
			<< endl;
		cin.clear();
		std::cin.ignore(numeric_limits<streamsize>::max(), '\n');
		
		}

		else
		correct = true;

I like this one much better.