Question

I’m trying to do a C-style string copy but something is not working right. What am I doing wrong?

#include <iostream>
using std::cout;
using std::cin;
using std::endl;
int main() {
    char string_a[20]="Good day!";
    char string_b[30]="Hi!";
    int i=0;
    cout << "string a: " << string_a << endl;
    cout << "string b: " << string_b << endl;
    while (*string_a++ = *string_b++) {
        cout << ++i << endl;
    }
    cout << "string a: " << string_a << endl;
    cout << "string b: " << string_b << endl;
    return 0;
}

Answer 1

You cannot do:

string_a++

if string_a is defined as an array. That only works for pointers and arrays decay to pointers only in specific circumstances.

If you change:

while (*string_a++ = *string_b++) {
    cout << ++i << endl;
}

into:

char *pa = string_a, *pb = string_b;     // a "specific circumstance" :-)
while (*pa++ = *pb++) {
    cout << ++i << endl;
}

then it will work just fine, outputting:

string a: Good day!
string b: Hi!
1
2
3
string a: Hi!
string b: Hi!