Help with multiple definition of main

Javinon (2)
I'm trying to write a code to determine whether a number is a "happy" number or not, this is the code I developed. Originally did it with the main function and then a function bool isHappy(unsigned int n), but I got the following error when compiling, which I'm still getting:

jcwa@Adkins-MSI:/mnt/d/code/exam1$ g++ -std=c++17 happy.cpp happy.cpp
/tmp/ccRfdsUm.o: In function `main':
happy.cpp:(.text+0x0): multiple definition of `main'
/tmp/cczezbZD.o:happy.cpp:(.text+0x0): first defined here
collect2: error: ld returned 1 exit status

Here is the code: 

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#include <iostream>
#include <vector>

using std::cin, std::cout, std::endl, std::vector;

int main() {
    cout << "Enter a number to check for happiness: " << endl;
    unsigned int n;
    cin >> n;
    vector<int> nums(0);
    int orig = n;
    bool happy = 0;
    int length = 0;
    int sqSum;
    for (int i = 0; n > 10; n/= 10) {
        nums.push_back(n % 10);
        length++;
        int check = n / 10;
        if (check <= 10) {
            nums.push_back(check);
            length++;
            for (int j = 0; j < length; j++) {
                sqSum += nums.at(j)*nums.at(j);
            }
            if (sqSum == 1) {
                happy = 1;
            } else if (sqSum == orig) {
                happy = 0;
            } else {
                n = sqSum;
            }
        }
    }
    if (happy == 1) {
        cout << n << " is a happy number." << endl;
    } else {
        cout << n << " is not a happy number." << endl;
    }
    return 0;
}


I haven't been able to do any testing to see if this code would actually work since I can't compile it, so I'm not looking for help with that, but why am I getting the multiple definitions error? This .cpp is saved in its own folder by itself.
Ganado (6849)
g++ -std=c++17 happy.cpp happy.cpp
You're compiling happy.cpp twice?

By the way, once you get past the compiler errors:
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 In function 'int main()':
15:14: warning: unused variable 'i' [-Wunused-variable]
23:47: warning: 'sqSum' may be used uninitialized in this function [-Wmaybe-uninitialized]
Last edited on
lastchance (6980)
Look at the compiler command that you give.

How many occurrences of happy.cpp are there?
Last edited on
Javinon (2)
Alright thanks I feel like an idiot now I was just confused by the way I was instructed to compile the first code that I made. It was never really explained to me very well how you're supposed to compile code, I was just given 1 example and was trying to figure it out based off of that. They made me compile the first code I wrote by typing "g++ -std=c++17 -o hello_world hello_world.cpp" so I thought you had to say the name of the file twice although I didn't know why. Still don't know what was going on there really. At least this issue is cleared up, thanks again

Final code that worked:

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#include <iostream>
#include <vector>

using std::cin, std::cout, std::endl, std::vector;

int main() {
    cout << "Enter a number to check for happiness: " << endl;
    unsigned int n;
    cin >> n;
    bool happy = 0;
    int last;
    int sqSum = 0;
    int orig = n;
    int count = 0;
    while ((sqSum != orig) && (sqSum != 1)) {
        last = n % 10;
        sqSum += last*last;
        if ((n < 10) && (sqSum != orig) && (sqSum != 1)) {
            n = sqSum;
            sqSum = 0;
        } else {
            n /= 10;
        }
    }
    if (sqSum == 1) {
        cout << orig << " is a happy number." << endl;
    } else {
        cout << orig << " is not a happy number." << endl;
    }
    return 0;
}
Last edited on
Ganado (6849)
-o (name) sets the name of the output file.
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