multiple initializations in for loop

Question

I am trying to write a function to find the average of numbers at first i wrote code as

double CPPLib::average_of_numbers(std::vector<int> &numbers){
    double result = -1;
    if(numbers.size() != 0)
    {
        result = 0;
        for(int i=0;i< int(numbers.size());i++)
        {
            result += numbers[i];
            std::cout << result << std::endl;
        }
        std::cout << result << std::endl;
        result = result/numbers.size();
        std::cout << result << std::endl;
    }
    return result;
}

for the input {1,2,3,4,5} the above code works fine and prints 1 3 6 10 15 15 3 3 .but when i tried to include the result = 0 in "for" loop initialization i am getting result as -1 after for loop.as shown in the code

double CPPLib::average_of_numbers(std::vector<int> &numbers){
    double result = -1;
    if(numbers.size() != 0)
    {
        
        for(int i=0,result = 0;i< int(numbers.size());i++)
        {
            result += numbers[i];
            std::cout << result << std::endl;
        }
        std::cout << result << std::endl;
        result = result/numbers.size();
        std::cout << result << std::endl;
    }
    return result;
}

result is displayed as 1 3 6 10 15 -1 -0.2 -0.2 can you please let me know the reason for this. Thank you so much.

return (numbers.empty() ? -1. : (std::accumulate(numbers.begin(), numbers.end(), 0.) / numbers.size());. — Jarod42
– Jarod42, Commented Jan 27, 2022 at 10:43
Like everywhere else int i=0,result = 0 declares two int variables. It's not one declaration with initializer and one assignment, separated by the comma operator. — molbdnilo
– molbdnilo, Commented Jan 27, 2022 at 10:45

selbie · Accepted Answer · 2022-01-27 10:40:58Z

4

In your second example, you've actually declared two separate variables called result. The first is here at the top of your function.

double result = -1;

The other is here:

    for(int i=0,result = 0;i< int(numbers.size());i++)

You've declared both a temporary int named result (in addition to i) who's lifetime and scope is within the for-loop. It overrides the outer result declared earlier. When the for-loop exits, references to result are back to the original variable declared earlier.

Easiest fix is to do what you were doing in your first example. Explicitly set result=0 outside the loop.

edited Jan 27, 2022 at 10:40

answered Jan 27, 2022 at 10:34

selbie

105k15 gold badges109 silver badges187 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

multiple initializations in for loop

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related