upper to lower and vice-versa without loop in C++?

Question

Input:

abcdE

Output:

ABCDe

I am looking for an efficient and less code solution for this code:

#include <iostream>   
#include <string>
using namespace std;

int main() {
    int len, ;
    string data;

    cin >> data;

    len = data.length();

    for (i = 0; i < len; i++)
        if (isupper(data[i]))
            data[i] = tolower(data[i]);
        else
            data[i] = toupper(data[i]);

    cout << data << endl;

    return 0;
}

Yeah, there is: [`std::ctype::toupper()`](http://en.cppreference.com/w/cpp/locale/ctype/toupper), you may apply that using a `std::transform()` algo or such. — πάντα ῥεῖ, Sep 30 '16 at 19:17
You might be able to write this in fewer lines but as for efficient this is O(N) and since you have to visit every element that as good as you can get. — NathanOliver, Sep 30 '16 at 19:19

score 2 · Accepted Answer · answered Sep 30 '16 at 19:23

2

I suppose you should use std::transform:

std::string str("abcdE");
std::transform(str.begin(), str.end(), str.begin(), [](char c) {
        return isupper(c) ? tolower(c) : toupper(c);
});

answered Sep 30 '16 at 19:23

Edgar Rokjān

17,245
4
40
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thats effectively a loop, but worse since instead of performing a cached block of code the way cpus are optimized, it performs an anonymous function call on every single character. It's like a loop but instead of doing X, you are calling a function on each iteration that does X. It also loses compatibility with older c++ versions. Quite a hefty price for cleverness. – Dmytro Jul 27 '19 at 02:49

nishantsingh · Answer 2 · 2016-09-30T19:36:19.223

0

You can also use std::for_each from algorithm library.

#include <iostream>   
#include <string>
#include <algorithm>

int main() {
    std::string data = "AbcDEf";
    std::for_each(data.begin(), data.end(), [](char& x){std::islower(x) ? x = std::toupper(x) : x = std::tolower(x);});
    std::cout << data<< std::endl;
}

edited Sep 30 '16 at 19:36

answered Sep 30 '16 at 19:26

nishantsingh

4,537
5
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1

Please do not use magic numbers for characters. C++ has the syntax to let you use the characters instead. – NathanOliver Sep 30 '16 at 19:29
@NathanOliver I suppose this makes you happy now. – nishantsingh Sep 30 '16 at 19:31
No but I will remove the down vote. AFAIK this is still a broken way to do it. – NathanOliver Sep 30 '16 at 19:32
And why do you feel so? – nishantsingh Sep 30 '16 at 19:32
1

There are other character sets besides ASCII than can be used for C++ and the letter blocks do not need to be contiguous. Only the number block is guaranteed to be contiguous. – NathanOliver Sep 30 '16 at 19:34
Agreed. Better to use the inbuilt functions. – nishantsingh Sep 30 '16 at 19:35

upper to lower and vice-versa without loop in C++?

2 Answers2