打印错误的值

Question

I am trying to build a program that outputs No. of people I have entered and the average of their ages. This is my code

#include <iostream>
#include <string>
using namespace std;

int main()
{
    int age;
    int total = 0;
    int No_of_People = 0;

    while (age != -1){
        total = total + age;
        No_of_People++;

        cout << "Enter a person's age or enter -1 to stop\n";
        cin >> age;
    }

    cout << "Number of people entered:\n" <<No_of_People<< endl;
    cout << "Average age of people = "<< total/No_of_People;

    return 0;
}

However the computer prints the average wrong, anyone know what i did wrong? This is the output

Answer 1

I see two major problems in your code: First, age is not initialized. Reading from it leads to undefined behavior (as mentioned by UnholySheep). Everything could happen from some seemingly random value to an access violation. I once forgot to initialize a boolean variable, it was initialized with false on my computer every time I ran the program (like I intended), on another team members it was initialized to true and we wondered why it's working for me but not for him. So best initialize it with 0 like you do for total .

Second, you're adding age on total before knowing its value. So when you set age to 0 in the beginning, you will increase the number of people one more time than you increase the total age. Add age to total after asking for a value.

A third thing is, that you don't take care for -1 properly. You're increasing the number of people even if -1 is typed in. You should check for that value before increasing the number of people or adding it to your total.

Answer 2

Just thought I would add to Tobias Brösamle's answer.

A good hint that you did not initialize age might be that running the program multiple times with the same input values yields different results.

Answer 3

Have a look at these modifications, comments highlight changed code.

Mostly I see that you're a beginner in coding, your errors can be attributed to not quite developing a "working methodology" - ie always initialising variables. I also moved the code into a separate function, whenever I put test code in a main function it very quickly develops into needing to do this anyway.

#include <string>
#include <iostream>

using namespace std;

void age()
{
    int age = 0;  // not initalised
    int total = 0;
    int count = -1; // naming convention of previous variable didn't match other variables

    do // loop terminates at bottom
    {               
        cout << "Enter a person's age or enter 0 to stop\n"; // why \n here instead of endl?
        cin >> age;

        total += age;
        count++;
    } while (age > 0); // slightly easier code to write if 0 terminates instead of -1

    cout << "Number of people entered:\n" << count << endl;
    cout << "Average age of people = " << total / (float)count; // floating point result
}

int main()
{
    age();

    char temp;
    cin >> temp;
}

Answer 4

you should copy the code

cout << "Enter a person's age or enter -1 to stop\n";
cin >> age;

before the while loop.