The 'for' not running well

Question

When I'm trying to run the program and execute it the for loop doesn't repeat of an adequate form, when I'm trying to execute it appears me this:

Enter a number:
5.6
Enter a number:
Enter a number:
Enter a number:
Enter a number:
Enter a number:
Enter a number:
Enter a number:
Enter a number:
Enter a number:

I tried to search some information about this problem, but I don't found anything. I know that is a foolish question but I don't know where else to turn. A help is appreciated. I left you my code:

#include <iostream>
using namespace std;
int main (void){
    int num, sum;
    float average;
    for(int i=0; i<10; i++){
        cout << " Enter a number: " <<endl;
        cin >>i;
        sum += num;
    }   
        average = num / 10;
        cout << " The total average is:\n " << media <<endl; 
}

You are not initializing `sum` or `num` before use, causing undefined behaviour. — Ulrich Eckhardt, Apr 10 '16 at 15:04
In addition to the previous comments, you probably also meant `average = sum / 10;` — Ami Tavory, Apr 10 '16 at 15:06
By the way, are you sure this compiles? It doesn't on my machine, because `media`. — Mr Lister, Apr 10 '16 at 15:06
And even if you correct all the errors, are you sure a float average of 10 integers makes sense? You'd end up with 2.4 children. — Mr Lister, Apr 10 '16 at 15:11
@MrLister what's exactly wrong with having 2.4 children in the average family? It's a good healthy number. — n. m. could be an AI, Apr 10 '16 at 15:15
@ Lưu Vĩnh Phúc for repeat in order to introduce a more number until to arrive to one that will not comply the condition. — V_WraMphT3R, Apr 10 '16 at 15:32

score 0 · Answer 1 · edited May 23 '17 at 11:45

0

cin fails its formatted input operation. It was expecting an integer, but you entered into it a floating point number. Hence, it failed. change the input to a float or double.

A couple of more problems with your code:

You can write int main(), rather int main(void). The void isn't quite useful here
Always initialize your variables before use
Sometimes, check for cin failures and report errors if need be

Corrected code...

#include <iostream>
using namespace std;
int main (){
    int num = 0, sum = 0;
    float average = 0;
    for(int i=0; i<10; i++){
        cout << " Enter a number: " <<endl;
        if(!(cin >> num)){   //you can also use a while loop to force requirement of proper input
             cin.clear();
             cin.ignore(100000, '\n');
             // you can print an error message here
        }
        else
             sum += num;
    }   
        average = static_cast<float>(sum) / 10;
        cout << " The total average is:\n " << average <<endl; 
}

See Why would we call cin.clear() and cin.ignore() after reading input?

edited May 23 '17 at 11:45

Community

1
1

answered Apr 10 '16 at 15:12

WhiZTiM

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@WhiZTiM !cin >> num, what does this do? doesn't ! have a higher precedence than >>? – Biruk Abebe Apr 10 '16 at 15:18
Cast `sum` to `float` before using division: `average = (float)sum / 10;` – Đăng Khoa Huỳnh Apr 10 '16 at 15:18
@juanchopanza, true... but that syntax was inherited in compatibility with `C` which meant a function with no argument because in C, `int main()` really means a function with a variable number of argument.... That doesn't hold for C++. See http://stackoverflow.com/questions/51032/is-there-a-difference-between-foovoid-and-foo-in-c-or-c – WhiZTiM Apr 10 '16 at 15:20
So what? You were suggesting something is wrong with that. In a post with so many genuine bugs, it seems confusing to talk about something that is fine as if it wasn't. – juanchopanza Apr 10 '16 at 15:21
@ĐăngKhoaHuỳnh, Thanks ^^ Corrected... |{|}| Thanks bkVnet, clarified – WhiZTiM Apr 10 '16 at 15:23
@juanchopanza, ... Well, you are right, but don't you think its good to point people to "more modern" ways? ... Nonetheless, I have corrected my use of strong "Don't use" – WhiZTiM Apr 10 '16 at 15:28

score 0 · Answer 2 · answered Apr 10 '16 at 19:46

You have three things that ain't correct:

First of all, you have to initialize sum before using, like so int sum = 0;.
Second of all, the entered number has to be saved in a variable. You can't use i as that variable 'cause it's you loop iterator, therefore you can use num.
Last of all, media has no meaning in your program. and i know you meant to use average.

After correcting all of these, your program should look like this one:

#include <iostream>
using namespace std;
int main (void){
    int num, sum=0;
    float average;
    for(int i=0; i<10; i++){
        cout << " Enter a number: ";
        cin >>num;
        sum += num;
    }   
    average = num / 10;
    cout << " The total average is:\n " << average <<endl; 
    system("pause");
}

The 'for' not running well

2 Answers2