why I didn't get my desire input?

[Violetzz]

Hello, I'm a beginner and I need to do a task about using functions. I already made the code as below, however, after it sums up all the number that I input, it just print out as "The sum of x is less than 100", even though I input the numbers as 90, 45 ,... can someone point out my logic mistakes? Thank you in advance !

 #include <iostream>

using namespace std;

void display(int x) {
    cout << "Welcome to the odd and even number counting program.\n";
}

void odd_or_even(int x) {
    if (x != 0) {
        //check if input value is odd or even number
        if ((x % 2) != 0) {
            cout << "You have just entered an ODD number.\n";
        }
        else
            cout << "You have just entered an EVEN number.\n";

    }
}

    int sum_of_num(int sum, int num) {
        sum += num;
        if (sum < 100)
            return 1;
        else
            return 2;
    }

    void display_sum(int sum) { // is there any problems with my logic here?
        if (sum > 100)
            cout << "The sum of x is more than 100.\n";
        else 
            cout << "The sum of x is less than 100.\n";

    }

   void thank_you() {
    cout << "Thank you for using this program.\n" ;
}

int main()
{
    int num;
    int sum = 0;
    int welcome = 0;

    display(welcome); //welcome messages
    cout << "This program is divided into 5 functions.\n";
    cout << "First part is to display welcome message using a function,\n " ;
    cout << "Second part is to check whether you have inserted an odd or even number using a function, \n" ;
    cout << "Third part is to check the limit of sum and return an integer to the main program.\n " ;
    cout << "Fourth part is to display the message of sum. \n" ;
    cout << "Last part is to display thank you message.\n " ;
    cout << "========================================== \n" ;

    do {
        cout << "Please, enter number (0 to exit): ";
        cin >> num;
        
        odd_or_even(num);
        sum_of_num(sum, num);
        }
     while (num != 0);
    //check if sum > 100 or < 100
    
   
   

    display_sum(sum);
    thank_you();


    cout << "=================================\n";
    

    


}

[keskiverto]

Look at http://www.cplusplus.com/doc/tutorial/functions/
It describes that function can take parameter by value or by reference.

// this function takes both parameters by value
int sum_of_num( int sum, int num );

Since the function simply copies the value of caller's argument, it will not modify the caller's argument.
If the function would use a reference to caller's argument, then the 'sum' in main() would be modified.


PS.

    // you call that function
    sum_of_num( sum, num );

The function returns an integer value. You don't use that value in any way.
Why does the function return a value? What is the purpose of that return value?

[Violetzz]

I use the return since the questions said to use the function like :

"Function name - int sum_of_x(int sum)- This function will get an integer
sum from main function and then check whether the summated integers is smaller
than 100 or larger than 100. It will return 1 if the sum value is larger than 100.
Otherwise, it will return 2."

[seeplus]

sum_of_num() returns a value, but this returned value is not used by the calling code

sum_of_num(sum, num);

you need something like:

int is100 = sum_of_num(sum, num);

and then test is100 and output an appropriate message.

Note that in sum_of_num function, sum should be passed by ref as it's value is changed in the function.

[Violetzz]

wait, what do you mean by test is100?

[seeplus]

int is100 = sum_of_num(sum, num);

if (is100 == 1)
   std::cout << "less than 100\n";
else
    std::cout << "100 or more\n";

the return value from sum_of_num is assigned to the variable is100 which is then tested in the if statement as the condition.

This is just an example. test and process as required.

[Violetzz]

I tried to do my functions something like this, but still, it print out sum of x < 100, even I entered 90, 34, 45,... whyy?? T_T

int sum_of_num(int sum, int num) {
    sum += num;
    if (sum > 100)
        return 1;
    else
        return 2;
}

    void display_sum(int sum) {
        {
            if (sum == 1)
                cout << "The sum of x is more than 100.\n";
            else
                cout << "The sum of x is less than 100.\n";
        }

    }

[seeplus]

sum needs to be passed by ref and not by value as per my previous post

int sum_of_num(int& sum, int num) {
    sum += num;

    if (sum > 100)
        return 1;
    else
        return 2;
}

[MikeyBoy]

Are you sure you're taking the return value of sum_of_num(), and passing that into display_sum()? Since you haven't shown us your modified main() function, there's no way for us to know.

EDIT: Also, you would help yourself and us if you used a sensible indentation style.

[Violetzz]

Oh, I'm sorry, this is my modified main function

#include <iostream>

using namespace std;

void display(int x) {
    cout << "Welcome to the odd and even number counting program.\n";
}

void odd_or_even(int x) {
    if (x != 0) {
        //check if input value is odd or even number
        if ((x % 2) != 0) {
            cout << "You have just entered an ODD number.\n";
        }
        else
            cout << "You have just entered an EVEN number.\n";

    }
}
int sum_of_num(int& sum, int num) {
    sum += num;
    if (sum > 100)
        return 1;
    else
        return 2;
}

    void display_sum(int sum) {
        {
            if (sum == 1)
                cout << "The sum of x is more than 100.\n";
            else
                cout << "The sum of x is less than 100.\n";
        }

    }

    

   void thank_you() {
    cout << "Thank you for using this program.\n" ;
}

int main()
{
    int num = 0;
    int sum = 0;
    int welcome = 0;

    display(welcome); //welcome messages
    cout << "This program is divided into 5 functions.\n";
    cout << "First part is to display welcome message using a function,\n " ;
    cout << "Second part is to check whether you have inserted an odd or even number using a function, \n" ;
    cout << "Third part is to check the limit of sum and return an integer to the main program.\n " ;
    cout << "Fourth part is to display the message of sum. \n" ;
    cout << "Last part is to display thank you message.\n " ;
    cout << "========================================== \n" ;

    

    do {
        cout << "Please, enter number (0 to exit): ";
        cin >> num;
        
        odd_or_even(num);
        
        sum_of_num (sum,num); // do you mean this part?
        display_sum(sum);

       
    } while (num != 0);
    
    thank_you();


    cout << "=================================\n";
   
}

[Violetzz]

wait, I just realized what do you mean by pass by ref, sorry for my silly mistakes T_T, I just started my programming last week, so there's a lot of thing that I confused. Btw thank you all for helping ^_^

[seeplus]

#include <iostream>

using namespace std;

void display()
{
	cout << "Welcome to the odd and even number counting program.\n";
}

void odd_or_even(int x)
{
	//check if input value is odd or even number
	if ((x % 2) != 0) {
		cout << "You have just entered an ODD number.\n";
	} else
		cout << "You have just entered an EVEN number.\n";
}

int sum_of_num(int& sum, int num)
{
	sum += num;

	if (sum > 100)
		return 1;
	else
		return 2;
}

void display_sum(int sum)
{
	if (sum == 1)
		cout << "The sum of x is more than 100.\n";
	else
		cout << "The sum of x is less than 100.\n";
}

void thank_you() {
	cout << "Thank you for using this program.\n";
}

int main()
{
	int num = 0;
	int sum = 0;

	display(); //welcome messages

	cout << "This program is divided into 5 functions.\n";
	cout << "First part is to display welcome message using a function,\n ";
	cout << "Second part is to check whether you have inserted an odd or even number using a function, \n";
	cout << "Third part is to check the limit of sum and return an integer to the main program.\n ";
	cout << "Fourth part is to display the message of sum. \n";
	cout << "Last part is to display thank you message.\n ";
	cout << "========================================== \n";

	do {
		cout << "Please, enter number (0 to exit): ";
		cin >> num;

		if (num != 0) {
			odd_or_even(num);

			int is100 = sum_of_num(sum, num);

			display_sum(is100);
			// or just
			//display_sum(sum_of_num(sum, num));
		}
	} while (num != 0);

	thank_you();

	cout << "=================================\n";
}

[MikeyBoy]

You don't need to worry about passing by reference for now. You just need to actually use the number that sum_of_num() returns.