find and replace a specific element of an array - c++

Question

I am trying to locate "empty" in the array Bob, then after I find where empty is in the index i want to replace the word "empty" with "LEEROY JENKINS" Please forgive my lack of knowledge I am still very new to this and learning the best I can.
Problems:
int spindex() is not finding the correct index
empty is not being replaced
#include <string>
#include <iostream>
using namespace std;
int spindex(string x[], int n)
{
int i = 0;
int tindex;
while (x[i] != "empty" && i < n)
{
tindex = i;
i++;
}
return tindex;
}
int main()
{
string Bob[] = { "shaun", "empty", "tom", "empty", "chris", "sharon", "empty"};
int pim = 7;
int Q = spindex(Bob, pim);
Bob[Q] = "LEEROY JENKINS";
cout << Q << endl;
cout << Bob[Q] << endl;
for (int i = 0; i < 7; i++) {
cout << Bob[i] << endl;
}
}

Answer 1

This function
int spindex(string x[], int n)
{
int i = 0;
int tindex;
while (x[i] != "empty" && i < n)
{
tindex = i;
i++;
}
return tindex;
}
is wrong. Except when the first element of the array has the value "empty" the function returns the index before the index of the element that contains the string.
Also the order of the sub-conditions in the condition of the while loop is also wrong.
Write it the following way
size_t spindex( const std::string a[], size_t n )
{
size_t i = 0;
while ( i < n && a[i] != "empty" ) i++;
return i;
}
and call it like
size_t Q = spindex( Bob, sizeof( Bob ) / sizeof( *Bob ) );
A more general approach to write the function looks the following way
size_t spindex( const std::string a[], size_t n, const std::string &s )
{
size_t i = 0;
while ( i < n && a[i] != s ) i++;
return i;
}
And it can be called like
size_t Q = spindex( Bob, sizeof( Bob ) / sizeof( *Bob ), "empty" );
As an alternative you could use standard algorithm std::find declared in the header <algorithm>.

Answer 2

The problem is the way you constructed your loop:
while (x[i] != "empty" && i < n)
{
tindex = i;
i++;
}
First, i is 0. tindex gets set to 0, i gets set to 1.
Then the loop repeats, checking the condition. Oops! x[1] is "empty"! The loop ends and tindex is still 0.
That's why Q is 0 and why the wrong element is replaced.
Furthermore, you check i < n after trying to use x[i] (whoops).
You might as well just return i, since that is already the value you need:
int spindex(string x[], int n)
{
int i = 0;
while (i < n && x[i] != "empty") {
i++;
}
return i;
}
(live demo)
In my opinion, the entire problem would be better constructed thus:
#include <string>
#include <algorithm>
#include <iostream>
int main()
{
std::string Bob[] = { "shaun", "empty", "tom", "empty", "chris", "sharon", "empty"};
auto it = std::find(std::begin(Bob), std::end(Bob), "empty");
if (it == std::end(Bob)) {
// No "empty" to replace!
return EXIT_FAILURE;
}
// Replace first "empty" with "BOB"
*it = "BOB";
// Here is our array now
std::cout << '[';
for (const auto el : Bob)
std::cout << el << ',';
std::cout << ']' << '\n';
}
// Output: [shaun,BOB,tom,empty,chris,sharon,empty,]
(live demo)