How do i make 2 inputs case insensitive in c++?

Question

cout << "Please enter colors for the two cuboids: " ;
cin >> color1 >> color2;


if ( color1 == color2)
    cout << "Color names cannot be the same, good bye..." << endl;

Like here I need to check if color 1 is equal to color2 for example rEd and RED should be considered the same but I should not use for loops to solve this is there any other way?

You can use `while` loop instead of `for` loops. `for(A; B; D) C` is almost equivalent to `A; while(B) { C D; }` — MikeCAT, Nov 06 '20 at 15:58
Should not use for loops? What's the reason for this? Are you doing some kind of quiz? — john, Nov 06 '20 at 15:59
@MikeCAT It's highly unlikely that will be accepted by whoever set the assignment. The spirit of the task is clearly to avoid loops altogether. — Asteroids With Wings, Nov 06 '20 at 16:00
You could use `std::transform` to convert your strings to lower case. But `std::transform` uses a for loop internally. Does that count? — john, Nov 06 '20 at 16:00
@AsteroidsWithWings It may be accepted if the task is for leaning `while` loop. — MikeCAT, Nov 06 '20 at 16:01
I guess you are supposed to use recursion. But rather than second guess, why not ask the person who set this problem what the intention is. — john, Nov 06 '20 at 16:01
You could use [boost::iequals](https://stackoverflow.com/a/315463/4641116). — Eljay, Nov 06 '20 at 16:06

john · Answer 1 · 2020-11-06T16:11:07.513

Here's a solution with no loops. It converts each character in the string to lower case before comparing them, and uses tail recursion to iterate over the string. I'm guessing this is the intention of the problem you've been set, though some would say that tail recursion is a loop as well.

#include <cctype>
#include <string>

bool string_eq_ci(const std::string& x, const std::string& y);
bool string_loop(const std::string& x, const std::string& y, size_t i);

    ...
    if (string_eq_ci(color1, color2)))
        cout << "Color names cannot be the same, good bye..." << endl;
    ...

bool string_eq_ci(const std::string& x, const std::string& y)
{
    return x.size() == y.size() && string_loop(x, y, 0);
}

bool string_loop(const std::string& x, const std::string& y, size_t i)
{
    return i == x.size() || (
            tolower(static_cast<unsigned char>(x[i])) == 
            tolower(static_cast<unsigned char>(y[i])) && 
        string_loop(x, y, i + 1));
}

score 0 · Answer 2 · answered Nov 06 '20 at 16:19

0

You can use either of:

Use strcasecmp(), for example:

if(strcasecmp(color1.c_str(), color2.c_str()) == 0) { .. equal colors.. }
Convert both colors to lowercase (or uppercase), and compare strings, as you wrote in your question.You can do it with std::toupper.

answered Nov 06 '20 at 16:19

olegarch

3,670
1
20
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Can you write me the code for second one? Every time i try it it says no suitable conversion from std::string to int although color is not an int. – Omar Assouma Nov 06 '20 at 17:27
Click link over the "std::toupper". – olegarch Nov 06 '20 at 21:22

Logman · Answer 3 · 2020-11-06T17:50:56.353

For English colors without any iteration (loops, recursion, etc.) (beside those of IO operations):

#include <iostream>

int main()
{
    std::string color1;
    std::string color2;

    std::cout << "Please enter colors for the two cuboids: " ;
    std::cin >> color1 >> color2;
    
    if ( (color1.size() == color2.size()) 
        && ( (color1.front() | 0x20) == (color2.front() | 0x20) )
        && ( (color1.back() | 0x20) == (color2.back() | 0x20) )
       )
        std::cout << "Color names cannot be the same, good bye..." << std::endl;
}

wandbox

Exclaimer:

This is a little bit of a joke. I did not check if this code works ok for all colors and it may be wrong. But even so there may be a way to write code without any iterations.

score 0 · Answer 4 · answered Nov 06 '20 at 18:07

Since your assignment requires you not to write loops, my guess is that you are expected to use algorithms instead. This is a good thing, since algorithms often convey the intent of the code better than loops can.

Here's a function copied directly from here that converts all the characters of a string to lowercase:

std::string str_tolower(std::string s) {
    std::transform(s.begin(), s.end(), s.begin(), 
                   [](unsigned char c){ return std::tolower(c); } 
                  );
    return s;
}

Now you can use this function in the comparison of the strings like this:

if (str_tolower(color1) == str_tolower(color2))
  // ...

How do i make 2 inputs case insensitive in c++?

4 Answers4