How to print error if number is incorrect?

[numbii]

Hi. I need help with my code. It takes an integer as a parameter and returns the sum of the digits of the integer. I want my program to test if the integer is not too big to store or negative. I just can't wrap my head around it. Please be so kind to help.

#include <climits>
#include <cmath>
#include <iostream>
using namespace std;
void sumOfNumber();
int main()
{
    char answer;
 
    do
    {
        sumOfNumber();
        cout << "\nOneMoreTime (Y/N) : ";
        cin >> answer;
 
    } while (answer == 'Y' || answer == 'y');
    return 0;
}
 
void sumOfNumber()
{
    int val, num, sum = 0;
    cout << "Enter the number : ";
    cin >> val;
    num = val;
    while (num != 0 && num <= INT_MAX)
    {
        sum = sum + num % 10;
        num = num / 10;
    }
    cout << "The sum of the digits of the given number is " << sum;
 
} 

[salem c]

> It takes an integer as a parameter and returns the sum of the digits of the integer
Then your prototype needs to be
int sumOfNumber(int number)

Neither the prompting for input nor the printing of the result should be inside your function.

Your main should be along the lines of

int num = getTheNumber();
int sum = sumOfNumber(num);
printTheResult(sum);

[numbii]

Hi, thank you for your response.
I don't think I understand...
What I need help is how to make it test and return an error when the integer is negative or too large?

[coder777]

Something like this:

    unsigned int val, num, sum = 0;
    cout << "Enter the number : ";
    while(!(cin >> val))
{
    cout << "\nInvalid Number. Try again: ";
    cin.clear(); // unset failbit
    cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // skip bad input
}

See:

https://en.cppreference.com/w/cpp/io/basic_istream/ignore

[numbii]

Hi. Thank you for response. Could someone help me with the full code? I don't seem to understand untill I see how it is built and I really have a hard time figuring it out for the past few days.

[numbii]

I can't use arrays nor strings in the task, nor if statements nor larger amount for testing the number. I do not know what other options I have

[JLBorges]

> I can't use arrays nor strings in the task, nor if statements

I presume you are not allowed to use a switch statement either.

Something like this perhaps (overuse the conditional operator):

#include <iostream>
#include <climits>

enum result_t { OK, NOT_A_NUMBER, NEGATIVE, TOO_BIG } ;

result_t get_number( int& n )
{
    n = 123456 ;
    return ( std::cin >> n && n < 0 ) ? NEGATIVE : // input successful, and number is less than zero
        ( n == 0 && std::cin.fail() ) ? NOT_A_NUMBER : // input failed, and number was set to zero
            ( n == INT_MAX && std::cin.fail() ) ? TOO_BIG : // input failed, and number was set to INT_MAX
                ( n == INT_MIN && std::cin.fail() ) ? NEGATIVE : // input failed, and number was set to INT_MIN
                    OK ; // fine: input successful, and number is non-negative
}

int sum_digits( int number ) // invariant: non-negative n
{ return number < 10 ? number : ( number%10 + sum_digits( number/10 ) ) ; }

int main()
{
    int number ;
    std::cout << "enter a non-negative integer: " ;
    const result_t result = get_number(number) ;

    result == NOT_A_NUMBER ? ( std::cout << "error: input is not a number\n" ) :
        result == NEGATIVE ? ( std::cout << "error: number is negative\n" ) :
            result == TOO_BIG ? ( std::cout << "error: number is too big\n" ) :
                ( std::cout << "sum of digits: " << sum_digits(number) << '\n' ) ;
}