I am trying to get the index of an element in a vector of strings, to use it as an index in another vector of int type, is this possible ?
Example:
vector <string> Names;
vector <int> Numbers;
...
// condition to check whether the name exists or not
if((find(Names.begin(), Names.end(), old_name_)) != Names.end())
{ // if yes
cout <<"Enter the new name."<< endl;
cin >> name;
replace(Names.begin(), Names.end(), old_name_, name);
}
Now I want to get the position of old_name in the Names vector, to use it in accessing certain element in Numbers vector. So that I can say:
Numbers[position] = 3 ; // or whatever value assigned here.
I tried using:
vector <string> :: const_iterator pos;
pos = (find(Names.begin(), Names.end(), old_name_))
Numbers[pos] = 3;
but obviously this doesn't work since pos is of type string !
This question is related to
c++
To get a position of an element in a vector knowing an iterator pointing to the element, simply subtract v.begin() from the iterator:
ptrdiff_t pos = find(Names.begin(), Names.end(), old_name_) - Names.begin();
Now you need to check pos against Names.size() to see if it is out of bounds or not:
if(pos >= Names.size()) {
//old_name_ not found
}
vector iterators behave in ways similar to array pointers; most of what you know about pointer arithmetic can be applied to vector iterators as well.
Starting with C++11 you can use std::distance in place of subtraction for both iterators and pointers:
ptrdiff_t pos = distance(Names.begin(), find(Names.begin(), Names.end(), old_name_));
If you want an index, you can use std::find in combination with std::distance.
auto it = std::find(Names.begin(), Names.end(), old_name_);
if (it == Names.end())
{
// name not in vector
} else
{
auto index = std::distance(Names.begin(), it);
}
I am a beginner so here is a beginners answer. The if in the for loop gives i which can then be used however needed such as Numbers[i] in another vector. Most is fluff for examples sake, the for/if really says it all.
int main(){
vector<string>names{"Sara", "Harold", "Frank", "Taylor", "Sasha", "Seymore"};
string req_name;
cout<<"Enter search name: "<<'\n';
cin>>req_name;
for(int i=0; i<=names.size()-1; ++i) {
if(names[i]==req_name){
cout<<"The index number for "<<req_name<<" is "<<i<<'\n';
return 0;
}
else if(names[i]!=req_name && i==names.size()-1) {
cout<<"That name is not an element in this vector"<<'\n';
} else {
continue;
}
}
Source: Stackoverflow.com