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Editorial Team
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Asked: 2026-05-15T05:42:54+00:00

I am new to C++ (just starting). I come from a Java background and

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I am new to C++ (just starting). I come from a Java background and I was trying out the following piece of code that would sum the numbers between 1 and 10 (inclusive) and then print out the sum:

/* 
 * File:   main.cpp
 * Author: omarestrella
 *
 * Created on June 7, 2010, 8:02 PM
 */

#include <cstdlib>
#include <iostream>

using namespace std;

int main() {
    int sum;

    for(int x = 1; x <= 10; x++) {
        sum += x;
    }

    cout << "The sum is: " << sum << endl;

    return 0;
}

When I ran it it kept printing 32822 for the sum. I knew the answer was supposed to be 55 and realized that its print the max value for a short (32767) plus 55. Changing

int sum;

to

int sum = 0;

would work (as it should, since the variable needs to be initialized!). Why does this behavior happen, though? Why doesnt the compiler warn you about something like this? I know Java screams at you when something isnt initialized.

Thank you.

Edit:
Im using g++. Here is the output from g++ –version:
Im on Mac OS X and am using g++.

nom24837c:~ omarestrella$ g++ --version
i686-apple-darwin10-g++-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5646)
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1 Answer

  1. Editorial Team

    Because it’s not part of the C++ standard. The variable will just take whatever value is currently sitting in the memory it’s assigned. This saves operations which can sometimes be unnecessary because the variable will be assigned a value later.

    It’s interesting to note and very important for Java/.Net programmers to note when switching to C/C++. A program written in C++ is native and machine-level. It is not running on a VM or a some other sort of framework. It is a collection of raw operations (for the most part). You do not have a virtual machine running in the background checking you variables and catching exceptions or segfaults for you. This is a big difference which can lead to a lot of confusion in the way C++ handles variables and memory, as opposed to Java or a .Net language. Hell, in .Net all your integers are implicitly initialised to 0!

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