A string problem

[TomRed]

I found a practice problem on these forums and was trying to write a program for it when I couldn't get it to work correctly.

The problem is as follows:

Strings are your friends, until they betray you.

Requires:
variables, data types, and numerical operators
basic input/output
logic (if statements, switch statements)
loops (for, while, do-while)
functions
strings & string functions


Write a program that asks for a user first name and last name separately.
The program must then store the users full name inside a single string and out put it to the string.
i.e.
Input:
John
Smith
Output:
John Smith

★ Modify the program so that it then replaces every a, e, i , o, u w/ the letter z.
i.e.
John Smith -> Jzhn Smzth

So I'm trying to solve the ★ problem and this is my code

#include <iostream>
#include <string>

using namespace std;

string replacer(char vowel, int nameSize, string fullName);

int main()
{
    string firstName, lastName, fullName;
    
    cout << "Please enter the first name:";
    cin >> firstName;
    cout << endl;
    
    cout << "Please enter the last name:";
    cin >> lastName;
    cout << endl;
    
    fullName = firstName + " " + lastName;
    
    cout << "The full name is " << fullName << ".\n";
    
    int nameLength = fullName.size();
    
    fullName = replacer('a', nameLength, fullName);
    fullName = replacer('e', nameLength, fullName);
    fullName = replacer('i', nameLength, fullName);
    fullName = replacer('o', nameLength, fullName);
    fullName = replacer('u', nameLength, fullName);
    
    cout << "\nAfter replacement, the full name is " << fullName << ".\n";
    
    return 0;
}

string replacer(char vowel, int nameSize, string fullName)
{
    for (int i = 0; i < nameSize; ++i)
    {
        if (fullName[i] = vowel)
            fullName[i] = 'z';
    }
    
    return fullName;
}

My problem seems to be that no matter what names I input, all the letters ultimately come out as 'z's instead of just the vowels. If I could get any help I would truly appreciate it.

Also, if there is a simpler way to write this code and any of you would be so kind to help, I would appreciate some posts of how this can be done.

[Zhuge]

You need to use == for comparison; a single = is for assignment. So you are always going into the if statement and assigning fullName[i] to 'z'.

[TomRed]

I make so many of these silly mistakes... thank you very much.

[Zhuge]

Better a silly mistake that's easily corrected than a hard-to-find bug. ;)