To search for a value in a vector we can use find, which returns an iterator pointing to the first value found in a vector which matches the value passed in. If an item is not in a vector, the returned iterator points to one past the end of the vector, myVec.end().

So in this example, if we want to know if mvValue is contained in myVec we can use:

if (find(myVec.begin(), myVec.end(), myValue) != myVec.end()){
  //myValue is in the vector
}
else {
  //myValue is not in the vector
}

find searches for myValue between the iterators myVec.begin() and myVec.end() and the return value, an iterator pointing to the found item is them compared with an iterator pointing to one past the end of the vector, the condition for not found. This can be reversed to use == instead of != should that make more sense for a particular use. We could also use iterators that point to subsets of the vector if we knew the region of the vector that our data should be found in:

if (find(myVec.begin()+3, myVec.begin()+9, myValue) != myVec.end()){
  //myValue is in the subset of the vector
}
else {
  //myValue is not in the subset of the vector
}

It is important to note that this will not cope with multiple items matching myVal and will always return the first match it finds.