reverse a string:

[jocdrew21]

I was browsing the web looking for simple yet fun programming challenges and crossed this one. I figured out how to reverse the string in place but I want it to read "blue is house the". I approached it in two ways for the heck of it. My idea was the second one, the first one I googled. I didn't know a simple rbegin() could do that, pretty neat.

I found the question here.http://www.techinterview.org Does anyone know of any other sites where I can find more?

#include <iostream>
#include <string>


int main(int argc, const char * argv[])
{

    std::string phrase = "The house is blue.";
    
    for (auto it = phrase.rbegin(); it!=phrase.rend(); ++it)
    {
        std::cout<<*it;
    }
    std::cout<<"\n";
    
    for (int i=0; i<phrase.length(); ++i)
    {
        std::cout<<phrase.at(phrase.length()-i-1);
    }
    
    
    return 0;
}

[oogabooga]

To reverse the string by words, you could perhaps use the string member function find_last_of() to search for spaces, and then use substr() to output the word. This will require two indices, one indicating the end of the word and the other the beginning.

Also,

argv should not be declared const (the strings it points to are modifiable).


Don't declare argc and argv if you're not using them (this leads to unused parameter warnings ... haven't you turned up your warning level?).

[jocdrew21]

I do not know how to do that. I will have to google it.
Honestly I don't even know what

int main(int argc, const char * argv[])

does. I understand main but not its parameters, my compiler always puts them there, I am using Xcode 4

[MutantJohn]

argc is the number of command line words and argv is the array that stores each one.

Consider this command :

./regulus -np 1 -bl 10

Here, argc is 5 (regulus, -np, 1, -bl, 10) and argv is regulus (0), -np (1), 1 (2), -bl (3), 10 (4).

Normally, people just type void or leave what's in-between the parentheses blank.

[jocdrew21]

whats the point of using them? So int

 main(void){ }

is fine? It will do the same thing?

[oogabooga]

whats the point of using them? So

int main(void){ }

is fine? It will do the same thing?

You don't need the word "void" there, but otherwise that's one of the forms that a standards-compliant (hosted) compiler must accept.

The other form allows you to accept arguments from the command line. Try calling the following like:
> progname hello world

Note: argv[0] contains the program name (if available). And argv[argc] will be a NULL pointer.

#include <iostream>

int main(int argc, char **argv) {
    for (int i = 0; i < argc; ++i)
        std::cout << argv[i] << '\n';
    return 0;
}

[jimblumberg]

Normally, people just type void or leave what's in-between the parentheses blank.

If you're talking about void main() then you would be incorrect. The function main must be defined to return an int (in all hosted environments). However if you're not going to use any command line arguments you should leave the argument list blank (in C you would use a void parameter).

int main(int argc,  char** argv) // C or C++
or
int main() // C++
or 
int main(void) // C

As for reversing the string you could consider using string streams to process the string pushing the words onto a stack. Then clear the string and pop the words off the stack and insert them into your string.

Jim

[jocdrew21]

iterate it to reverse, use the stacks first in last out (FILO), then read the spaces with popping. Genius and so simple.... Thanks...

I am going to have to google the main() question. I know it has to be a int and return an int. I have seen people use argc in there programs before but I never looked into it. I think it is about time I do.

[Ewiv]

iterate it to reverse, use the stacks first in last out (FILO), then read the spaces with popping. Genius and so simple.... Thanks...

I am going to have to google the main() question. I know it has to be a int and return an int. I have seen people use argc in there programs before but I never looked into it. I think it is about time I do.

As was said it lets you take arguments into your main function and do something with them. Games use this often to set screen size etc on the fly based on a script file that the user can then change in the options menu.

As usual when you pass an array you pass the size of the array so that the function knows how many items are in it so you dont go past the array hence the first argument is the size of the argument array while the 2nd is a pointer to the array itself.