Ivalue annoyance

Been moving thru Accelerated C++ and I’m a little far thru, this problem annoys me though. This is the program that you make in chapter 2 which adds a frame to an inputted name etc etc Also says hello. Dev C++ says that there’s an error with it. Being that there is no I value in the assignment. The line under the comment: are we on the border?. Can someone help me with this I always seem to trip up on the I value stuff. Can I get an explanation on it as well for future reference. Thanks very much.

Code:

#include<iostream>
#include<string>

//say what standard-library names we use
using std::cin;          using std::endl;
using std::cout;         using std::string;

int main()
{
    //ask for persons name
    cout<<"Please enter your first name: ";
    
    //read the name
    string name;
    cin>>name;
    
    //build the message that we intend to write
    const string greeting="Hello, "+name+ "!";
    
    //the number of blanks surrounding the greeting
    const int pad=1;
    
    //the number of rows and columns to write
    const int rows=pad *2 +3;
    const string::size_type cols=greeting.size() + pad * 2 + 3;
    
    //write blank line of seperation
    cout<<endl;
    
    //write rows rows output
    //invariant:we have written r rows so far
    for(int r=0; r !=rows; ++r){
            
            string::size_type c=0;
            
            //invariant: we have written c characters so far in the current row
            while(c !=cols){
                    
                    //is it time to write the greeting?
                    if(r==pad + 1 && c==pad + 1){
                              cout<<greeting;
                              c +=greeting.size();
                    }else{
                          
                          //are we on the border?
                          if(r==0||r==rows-1||c==0||c=cols-1)
                          cout<<"*";
                    else
                      cout<<" ";
                    ++c;
                    }
            }
            
            cout<<endl;
    }
    return 0;
}

Code:

 if(r==0||r==rows-1||c==0||c == cols-1)

> if(r==0||r==rows-1||c==0||c=cols-1)
Perhaphs it's the missing = in c == cols-1

It's L-Value(elle-value) not I-Value(eye-value). The L stands for left. A left-value is a value that can appear on the left side of an assignment (left = right). The reason that you get a non l-value warning on this line:

Code:

if(r==0||r==rows-1||c==0||c=cols-1)

is because of the C order of precedence. The logical OR operator ( || ) has a higher precedence than the assignment operator ( = ). We can add brackets to show how the compiler tries to evaluate this line:

Code:

if( ((((r==0) || (r==rows-1)) || (r==0)) || c) = (cols-1) )

Obviously, we can see that the value on the left side of the assignment operator (highlighted) is not an l-value. Assuming we really wanted to do an assignment we could add brackets to force the correct order of precedence:

Code:

 if(r==0||r==rows-1||c==0|| (c=cols-1))