why output is giving 1 answer

Output is not giving right answer because 'if(a=1)' condition is right then it show the output is 5 Here is my code:

 #include<iostream>
        using namespace std;
        int main()
        {
            int a=5;
            if(a=1)
        {
            cout<<a;
        }
        else
        {
            cout<<"helloworld"<<endl;
        }
        return 0;
        }