Upper case letters

how can I write a program that converts upper case letters to lower case letters?

All characters are integers and one way to see their values is to goole "ascii table":
http://www.asciitable.com/index/asciifull.gif

In code, you can do:

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char ch = 'a';
std::cout << (int)ch << '\n';

So the trick is to do the correct math to switch upper to lower.

Last edited on

MiiNiPaa (8886)

Character set is implementaton defined (standard 3.9.1.1) and such math is non-portable.
there is tolower() function in <cctype> header

closed account (3qX21hU5)

I would use tolower() and toupper() like MiiNiPaa suggested. Here is a example, you iterator through the string and convert each character to uppercase or lowercase character by character. You can do this by using a iterator or using indexes.

#include <iostream>
#include <string>
#include <cctype>

using namespace std;

int main ()
{
    string words ("Hello how are you");

    cout << "Normal: " << words << endl;

    for (string::iterator it = words.begin(); it != words.end(); ++it)
       *it = toupper(*it);

    cout << "All Upper case: " << words << endl;

    for (string::size_type i = 0; i != words.size(); ++i)
        words[i] = tolower(words[i]);

    cout << "All lower case: " << words << endl;

    return 0;
}

Last edited on

Lim Boon Jye (157)

u can create a function

void stringtoUpper( string &s ){
    for( int i = 0 ; i < s.length() ; i++ ){
        s[i] = toupper(s[i]);
    }
}

it's more efficient
and include this

#include <ctype.h>

MiiNiPaa (8886)

You can do this by using a iterator

Why not range-based loops?

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for(char& x: words) {
    x = tolower(x);
}

and include this
#include <ctype.h>

<cctype>, .h versions of headers are deprecated.

closed account (3qX21hU5)

I was thinking about showing ranged based loops in the example but didn't want to complicate it to much for the OP since he is still learning (I believe though I might be wrong), and because of the possibility that he is using a non C++11 compiler.

Lowest0ne (1536)

Character set is implementaton defined (standard 3.9.1.1) and such math is non-portable.

If your c/c++ compiler isnt using the ASCII character set, you've got issues.

Also:
std::transform(str.begin(), str.end(), str.begin(), toupper);

But that sort of takes the whole learning aspect out of it.

Last edited on

giblit (3750)

You can also do this

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    string words = "HeLLo WOrLd";
    for(unsigned int i = 0; i<words.size(); i++) words[i] = tolower(words[i]);

EDIT: forget what I said I didn't realize Lim Boon Jye said pretty much same exact thing

Last edited on

MiiNiPaa (8886)

If your c/c++ compiler isnt using the ASCII character set, you've got issues.

Welcome to the world of ~~pain~~ locale codepages: http://en.wikipedia.org/wiki/Code_page_866 or "standard" http://en.wikipedia.org/wiki/KOI8-R — look at the letter 'Ё' (B3) and switched order of lowercase-uppercase letters in english and russian.
Also in local train station display controller uses codepage like "'\0' 1234567890AaBbCc/*...*/АаБбВв/*...punctuation and other*/"

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Upper case letters