Member Avatar for artisabang

I know how to generate numbers like 1-20, 1-1000 etc...
but Im trying to figure out how to generate random letters from A-Z?
any help please?

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Dani AI

Generated

If you just need random A-Z letters, prefer C++11’s <random> facilities over rand(). They give uniform distribution without modulo bias and avoid reseeding pitfalls.

#include <random>
#include <iostream>

char random_upper_letter() {
    static std::mt19937 rng(std::random_device{}());        // seed once
    static std::uniform_int_distribution<int> dist(0, 25);  // uniform over 26 letters
    return static_cast<char>('A' + dist(rng));               // ASCII/Unicode assumption
}

int main() {
    for (int i = 0; i < 3; ++i) std::cout << random_upper_letter() << ' ';
    std::cout << '\n';
}

Notes and tips:

  • The mapping 'A' + n assumes an ASCII/Unicode-like encoding where letters are contiguous, which is true on virtually all modern systems. For strict portability across exotic encodings, index into an explicit alphabet you define (e.g., an array of allowed characters).
  • If you want lowercase, change 'A' to 'a'. For mixed case, flip a std::bernoulli_distribution to decide case, then add 0 or 32 accordingly.
  • Avoid rand() % 26; it introduces bias unless you do rejection sampling, and rand() has weak statistical quality. See uniform_int_distribution and the overview of <random> at cppreference. For background on rand() limitations, see std::rand.

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Member Avatar for vijayan121

define a string literal

const char* const a_to_z = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" ;

generate a random integer ri in the range 0 to 25 (inclusive).
use a_to_z[ri] as the random letter.
note: *do not* do this: char( 'A' + ri )

Member Avatar for artisabang

hmm i dont seem to get it. btw im new to C++ :P

heres the code that I used to generate 3 random numbers

#include <iostream>
#include <cmath>
#include <ctime>

using namespace std;

int main()

{

unsigned seed = time (0);
srand (seed);

cout << rand() << " " << rand() << " " << rand() << " " << endl;

system("pause");
return 0;

}

where do i put the codes i need to generate letters instead?

Edited by happygeek because: fixed formatting
Member Avatar for Ancient Dragon

Look at an -- the letters 'A' - 'Z' have decimal values of 65 - 90. So just generate a random number between 0 and 26 then add 65.

Member Avatar for artisabang

i cant seem to get it lol eek!
can you just hook me up with the code?

Member Avatar for vmanes

<snip>
note: *do not* do this: char( 'A' + ri )

I'm curious why you say this?

Member Avatar for sarehu

note: *do not* do this: char( 'A' + ri )

Vijayan is saying this because it is not guaranteed that the character set will have the alphabetical characters 'A' through 'Z' or 'a' through 'z' represented by a contiguous block of integers. However, it is very likely. Some character set uses something like the ordering AaBbCc...Zz , which does not actually provide a sufficient lexicographical ordering, and EBCDIC has letters all over the place. But char('A' + ri) will probably work for you, and if it doesn't, you deserve so for having used such a bizarre character set. :D

commented: Nice clear response +2
Member Avatar for Ancient Dragon 
int main()
{
    int n = rand() % 26;
    char c = (char)(n+65);
    cout << c << "\n";
    return 0;
}
commented: Thanks, You were very clear and percise, it was very easy to understand. +0
Member Avatar for vmanes

i cant seem to get it lol eek!
can you just hook me up with the code?

We don't generally "just hook you up with the code." You make an attempt, show us your work, and we'll help you sort it out. You've been give two (or three) suggestions on how to solve your problem.

Member Avatar for Ancient Dragon

Vijayan is saying this because it is not guaranteed that the character set will have the alphabetical characters 'A' through 'Z'or 'a' through 'z' represented by a contiguous block of integers

Although correct, I have never seen such an operating system, but there could be one or more very obscure os's that have that quality.

Member Avatar for vmanes

Vijayan is saying this because it is not guaranteed that the character set will have the alphabetical characters 'A' through 'Z' or 'a' through 'z' represented by a contiguous block of integers. However, it is very likely. Some character set uses something like the ordering AaBbCc...Zz , which does not actually provide a sufficient lexicographical ordering, and EBCDIC has letters all over the place. But char('A' + ri) will probably work for you, and if it doesn't, you deserve so for having used such a bizarre character set. :D

Good points. It's been soooo long since I've seen EBCDIC, I'd forgotten that it isn't in contiguous sequences (only dealt with any such system for one two semesters, about 20 years ago).

Member Avatar for vijayan121

EBCDIC is by no means dead and buried. IBM's flagship operating systems z/OS http://www-03.ibm.com/systems/z/os/zos/index.html and i5/OS http://www-03.ibm.com/systems/i/os/i5os/ use EBCDIC
IBM's older mainframe operating syatems like OS/390, VM and VSE, and minicomputer operating systems like OS/400 also use EBCDIC.
non-IBM operating systems that use EBCDIC are rare; Fujitsu-Siemens' BS2000/OSD, Unisys MCP, HP MPE/iX etc.

Member Avatar for skatamatic

You can always just use the ascii values of the letters you want, combine it with your knowledge of random numbers and presto.

int Random(max, min) -> some random number function

int main
{
cout << char(Random(60, 40));
return 0;
}

im not too sure the exact ascii values of the alphabet, but you can easily look up a chart on google. Good luck!

Member Avatar for WaltP

Although correct, I have never seen such an operating system, but there could be one or more very obscure os's that have that quality.

Which is why you can ignore this advice. I've never seen (at least in the past 25 years) a system that a student uses that has a non-contiguous alphabet.

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