How to replace specific values in a vector in C++?

Question

I have a vector with some values (3, 3, 6, 4, 9, 6, 1, 4, 6, 6, 7, 3), and I want to replace each 3 with a 54 or each 6 with a 1, for example and so on.

So I need to

Answer 1

Use the STL algorithm for_each. It is not required to loop, and you can do it in one shot with a function object as shown below.

http://en.cppreference.com/w/cpp/algorithm/for_each

Example:

#include 
#include 
#include 
#include 
using namespace std;

void myfunction(int & i)
{
    if (i==3)
        i=54;
    if (i==6)
        i=1;
}


int main()
{
    vector v;
    v.push_back(3);
    v.push_back(3);
    v.push_back(33);
    v.push_back(6);
    v.push_back(6);
    v.push_back(66);
    v.push_back(77);
    ostream_iterator printit(cout, " ");

    cout << "Before replacing" << endl;
    copy(v.begin(), v.end(), printit);

    for_each(v.begin(), v.end(), myfunction)
        ;

    cout << endl;
    cout << "After replacing" << endl;
    copy(v.begin(), v.end(), printit);
    cout << endl;
}

Output:

Before replacing
3 3 33 6 6 66 77
After replacing
54 54 33 1 1 66 77