如何为向量编写 if 和 else 语句？

Question

I would like to know how i can write an if and else statement for a vector. So let's say i have a vector which includes 1,2,3,4,5. I want the if statement to return a string if the number 1 is inside the vector. I know how to structure it but how do i write the statement. I have writen an example below with question marks because I'm unsure what is supposed to be in the brackets.

vector <int> myvec {1,2,3,4,5};
if (myvec??? 1) [
cout << "yes it is there" << endl;

]

Answer 1

You might use std::find :

std::vector<int> myvec {1,2,3,4,5};
if (std::find(myvec.begin(), myvec.end(), 1) != myvec.end()) {
    cout << "yes it is there" << endl;
}

Answer 2

Various options. One is

 if (std::count(myvec.begin(), myvec.end(), 1) > 0)
 {
      cout << "yes it is there" << endl;
 }

This will detect the presence of one or more elements with value 1 . If you want to test if there is exactly one element with value 1 , change the > 0 to == 1 .

Answer 3

You can use:

if (std::find(myvec.begin(), myvec.end(), 1) != myvec.end()) {
   ...
}

I think it will be better to use a function that expresses what you want to do.

if ( vector_contains_item(myvec, 1) ) {
   ...
}

You push the details of the logic to the function.

bool vector_contains_item(std::vector<int> const& myvec, int item)
{
    return (std::find(myvec.begin(), myvec.end(), item) != myvec.end());
}