String manipulation

[Maerle]

How do you change a letter of a string to another and how do you invert the letters of a string?

Exemple:
Francisco -> FrXncXscX
Francisco -> ocsicnarF

[PiMaster]

To change a letter in a string:

1 2 3 4 5 6 7

char* str="The bird called to its mate"; //change the letters str[4]='g'; str[5]='o'; str[6]='a'; str[7]='t'; cout<<str;

The goat called to its mate

To invert a string, you would need to use the concept above in a function:

char* reverse(char* str){
    unsigned size=strlen(str);
    unsigned x;
    for(x=0;x<size;++x,--size){
        str[x]^=str[size];
        str[size]^=str[x];
        str[x]^=str[size];}
    return str;}

[Maerle]

Isn't there a string function for this problem? I'm doing the exercise of the forum 'Strings are your friends, until they betray you'. The question says that strings and string functions are requirable.

[Zhuge]

I would use find() and replace() if you want to be generic, and reverse iterators (rbegin(), rend()) to go backwards.

[rocketboy9000]

char* reverse(char* str){
    unsigned size=strlen(str);
    unsigned x;
    for(x=0;x<size;++x,--size){
        str[x]^=str[size]; //NOOO!!
        str[size]^=str[x]; //WHYY??
        str[x]^=str[size];}//AAAA!!
    return str;}

What the heck is this? I see that it must work, but why this convoluted bit logic?

[ne555]

so you don't need an extra variable.
And I think that the xor operation is shorter and faster than move.

If it is encapsulated, who cares? You will need to provide the ^= operator for user types (that doesn't make sense).

you could create a replace_if with transform.
or just loop over your string with find_first_of

[rocketboy9000]

Well, with the variable it can be optimized to a XCHG instruction with a register. Yours is too un-obvious for that.

[rocketboy9000]

Ok. I've gprof'd it and I surrender.
given this code

#include <string.h> 

char* weirdstrrev(char* str){
    unsigned size=strlen(str);
    unsigned x;
    for(x=0;x<size;++x,--size){
        str[x]^=str[size]; //NOOO!!
        str[size]^=str[x]; //WHYY??
        str[x]^=str[size];}//AAAA!!
    return str;}
    
char* normalstrrev(char* str){
	unsigned size=strlen(str);
	unsigned x;
	for(x=0;x<size;++x,--size){char c=str[x];str[x]=str[size];str[size]=c;}
	return str;
}

int main(void)
{
	char x[30]="this is a test of the swap.";
	register int i=100000000;
	while(i--)weirdstrrev(x);
	i=100000000;
	while(i--)normalstrrev(x);
}

with O2 optimization,
gprof shows your code is 7% faster:

Each sample counts as 0.01 seconds.
  %   cumulative   self              self     total           
 time   seconds   seconds    calls  ns/call  ns/call  name    
 39.34      0.72     0.72 100000000     7.20     7.20  normalstrrev
 36.61      1.39     0.67 100000000     6.70     6.70  weirdstrrev
 24.04      1.83     0.44                             main
-----------------------------------------------

[Maerle]

Here is the program. It's very complicated by the fact of string be a class we can't see. Does someone known an easier way?

#include <iostream>
#include <conio.h>
#include <string>

using namespace std;

int main() {
    string firstname, lastname;
    size_t found;
    
    cout << "Enter your first name: ";
    cin >> firstname;
    cout <<  "Enter your last name: ";
    cin >>  lastname;
    
    cout << "\n";
    
    string::reverse_iterator rit;
    for (rit = lastname.rbegin(); rit < lastname.rend(); rit++)
        cout << *rit;
    cout << " ";
    for (rit = firstname.rbegin(); rit < firstname.rend(); rit++)
        cout << *rit;
    
    cout << "\n";
    
    cout << "\n" << firstname << " " << lastname << endl;
    
    found = firstname.find_first_of("aeiou");
          while (found != string::npos) {
                firstname[found] = 'z';
                found = firstname.find_first_of("aeiou", found + 1);
          }
    found = lastname.find_first_of("aeiou");
          while (found != string::npos) {
                lastname[found] = 'z';
                found = lastname.find_first_of("aeiou", found + 1);
          }
          
    cout << firstname << " " << lastname << endl;
    
    getch();
    return 0;
}

[ne555]

seems familiar: http://www.cplusplus.com/forum/beginner/33124/#msg178184
Dunno if there is a "simpler" way, but your code will be cleaner if you create a function.

void subs( std::string &, const std::string &, char );

subs( firstname, "aeiou", 'z' );
subs( lastname, "aeiou", 'z' );