QUESTION:
Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
You can return the answer in any order.

Example 1:

Input: nums = [2,7,11,15], target = 9
Output: [0,1]
Explanation: Because nums[0] + nums[1] == 9, we return [0, 1].

if needed more you can visit the questions = (https://leetcode.com/problems/two-sum/description/)

I have solved this question with brute force solution however i am facing issues in c++ concept or maybe some basic interpretting issue.

My code:

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int n = nums.size();
        vector<int> ans;
        for ( int i = 0; i < n; i++){
            for ( int j = i+1; j < n ; j++){
                if ( nums[i] + nums[j] == target){
                    ans.push_back(i);
                    ans.push_back(j);
                    return ans;
                }
            }
        }
        
    }
};

However this solution is not showing compiling error =

Line 16: Char 5: error: non-void function does not return a value in all control paths [-Werror,-Wreturn-type]
   16 |     }
      |     ^
1 error generated.

So I prepared another solution which is working but i cant figure out the reason why the previous code is not working and this is.

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int n = nums.size();
        vector<int> ans;
        for ( int i = 0; i < n; i++){
            for ( int j = i+1; j < n ; j++){
                if ( nums[i] + nums[j] == target){
                    ans.push_back(i);
                    ans.push_back(j);
                }
            }
        }
        return ans;
    }
};

Somebody please explain the logic.

edit: i have done the dry run and for every input it is necessary that if ( nums[i] + nums[j] == target) will be executed and a return value will be given