如果else语句混淆了c ++

Question

#include <iostream>
using namespace std;

int main()
{
    int positiveInteger;

    cout << "Please input an integer up to 100." << endl;

    cin >> positiveInteger;

    int result = 0;
    for (int i = 0; i <= positiveInteger; i++)
    {
        if ( positiveInteger >= 0 )
        {
          result += i;
        }
        else 
        {
          cout << "Please input a positive integer." << endl;
        }
    }

    cout << result;
    return 0;
}

Above I have a for loop with an if else statement in the center. I am confused because I want it to be so when I enter a integer that is not negative it will loop the if result. But I want it to be so if I put in a negative number it says please input a positive integer. That's why I set it so in the if statement only numbers above and = to 0 would return the result, but if I enter a negative number I just get 0 I want it to say "Please input a positive integer". I don't understand what I'm doing wrong. Isn't the if statement if true pulls the if and if its not true pulls the else? Or am I missing something?

Answer 1

If you enter a negative number, you never get to enter the loop. An approach that fits better to such cases is:

do
{
    input a number;
    if( positive )
         do something;
} while( not positive );

Answer 2

If I got it right, you want to 1. input a number; 2.1 If the number is positive you loop through it. 2.2 If it's negative you show the error message.

The problem is your loop, where the conditional is, checks if i (which is zero) is smaller then the number. However if you input a negative number i will be bigger then positiveInteger and you won't loop through the if. I fixed your code

using namespace std;

int main()
{
    int positiveInteger;

    cout << "Please input an integer up to 100." << endl;

    cin >> positiveInteger;

    int result = 0;
    if ( positiveInteger >= 0 ){
       for (int i = 0; i <= positiveInteger; i++)
       {
           result += i;
       }
       cout << result;
    }
    else {
        cout << "Please input a positive integer." << endl;
    }

    return 0;

}

Answer 3

I think your code would benefit from some rearrangement. I'd structure it something like this:

do { 
    cout << "please enter a number between 1 and 100";
    number = get_number():
} while (number < 1 || number > 100);

cout << sum_series(1, number);

Answer 4

The output you are getting is because your loop fails at non-negative numbers. You should try the following:

int main()
{

int positiveInteger;

cout << "Please input an integer upto 100." << endl;

cin >> positiveInteger;

int result = 0;
if ( positiveInteger < 0 )
{

    cout << "Please input a positive integer." << endl;

}
else{


   for (int i = 0; i <= positiveInteger; i++)
   {

    result += i;

   }

 cout << result;

 }
return 0;

}

Answer 5

From my understanding, if the number is negative, you wish to take another input. But the cin statement is not under loop control to do it so. It just executes only one time irrespective of the nature of the number.