overflow when attempting to push_back randomly generated numbers in a vector

Question

my code is shown here:

#include <iostream>
#include <vector>
#include <string>
#include <stdlib.h>
using std::string;
using std::endl;
using std::cout;
using std::cin;

struct funcs
{
    std::vector<int> values;
    int sum;
    void createVectorValues(){
        while(values.size() < 100)
        {
            int x = rand() % 100;
            values.push_back(x);
        }
        for(int& a : values)
        {
            sum += 1;
        }
        cout << sum;

    }
};
int main()
{
    srand;
    funcs myFunct;
    myFunct.createVectorValues();
    
}

the following code results in a large value such as -858993360

How can I change this code so that it can function properly

_`&funcs::createVectorValues;`_ I am afraid this statement doesn't do what you think it does. Can you elaborate about what you thought please.? — πάντα ῥεῖ, Nov 26 '21 at 21:50
You need to create a `funcs` object then call the function: `funcs f; f.createVectorValues();` — 001, Nov 26 '21 at 21:54
@JohnnyMopp calling `srand()` once at the beginning of `main ()` would also be a good idea. — πάντα ῥεῖ, Nov 26 '21 at 21:58
Bah. `rand` is for pansies. The cool kids all use `std::uniform_int_distribution` from the [ library.](https://en.cppreference.com/w/cpp/header/random) — user4581301, Nov 26 '21 at 22:03
[`std::generate`](https://en.cppreference.com/w/cpp/algorithm/generate) could come in handy. — user4581301, Nov 26 '21 at 22:11
1) `sum` is not initialized, it's value is indeterminated and incrementing it is pointless. 2) What do you *really* want to sum? — Bob__, Nov 26 '21 at 23:55

score 0 · Answer 1 · answered Nov 26 '21 at 22:10

0

Try this:

int main(int, char **) {
    funcs myFunct;
    myFunct.createVectorValues();
}

Although no idea why your antivirus is involved. That might be a separate issue.

answered Nov 26 '21 at 22:10

Joseph Larson

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There's no "try", either your answer solves the OPs problem or not. – πάντα ῥεῖ Nov 26 '21 at 22:22
Well, given that I don't know a thing about his antivirus system -- and he didn't talk about it -- I guess I could have skipped giving him a solution that at least would get him closer. – Joseph Larson Nov 27 '21 at 00:34

score 0 · Accepted Answer · answered Nov 26 '21 at 23:54

You didn't define a constructor for funcs, so you get the default constructor, which invokes the default constructor of each member. This means the int member sum is left with an indeterminate value. See Does the default constructor initialize built-in types?. You probably want to write a constructor that initializes sum to 0.
srand; isn't a function call. It's valid syntax, because srand evaluates to a pointer to the srand function, but it's an expression with no side effects, so it does nothing. Much as if you had written 3;. To call the function, you need srand(arg), where arg is an appropriate integer. Or, switch to the C++11 random number generation features, which are much more powerful and usually have better randomness.

overflow when attempting to push_back randomly generated numbers in a vector

2 Answers2