C++ Printing a string in reverse using a for loop

Question

I have a program that prints out the characters of a string using a for-loop. It must also print the same characters in reverse, which is where I\'m having problems. Can someone

Answer 1

@Lokno already provided you with the correct answer. However, let me nitpick your code a bit more to show you some other alternatives and to correct some minor mistakes.

First, you didn't actually post a compiling example, because you forgot to show the included headers and and also didn't show the using namespace std; that was implicit in your code.

Second, for the regular for loop, prefer to keep the loop variable inside the loop, unless you actually need to use it as a return value. Also prefer pre-increment ++i over post-increment i++. Furthermore, because you have made sure of the correct loop indices, there is no reason to use the bounds-checked element access at() over the unchecked [] version.

In C++11, you have the range-for loop which allows for even shorter and more fool-proof code, where I also used auto where you could have used char. Unfortunately, there is no reverse range-for loop. The correct index-based reverse for loop is probably easier to read if you use i >= 0 rather than i > -1.

Then there is an algorithm based loop using std::copy where you use the iterator interface of std::string (in particular the reverse iterators rbegin() and rend()) to copy each character through an ostream_iterator that is bound to standard output.

BTW, I used the separator "|" rather than the newline to see stuff more easier, adapt to your taste. In any case, using std::endl can have performance implications because it flushes the output buffer every time.

#include 
#include 
#include  // you forgot this
#include    // you forgot this

int main()
{
    using namespace std;    // you forgot this

    // let's pretend this is the string
    string myAnimal = "Please enter the name of your favorite animal.";

    // keep the loop variable local, prefer pre-increment
    for (int i = 0; i < myAnimal.length(); ++i)
        cout << myAnimal[i] << "|";    // prefer [] over at()
    std::cout << "\n";

    // C++11 range-for
    for (auto c : myAnimal)
        std::cout << c << "|";
    std::cout << "\n";

    // index-based reverse loop
    for (int i = myAnimal.length() - 1; i >= 0; --i)
        cout << myAnimal[i] << "|";
    std::cout << "\n";

    // algorithm-based reverse loop
    std::copy(myAnimal.rbegin(), myAnimal.rend(), ostream_iterator(cout, "|"));
    std::cout << "\n";

    // main implicitly return 0
}

Live Example. PS: main() implicitly returns 0 upon success.