如何获得我的代码以随机打印字符或字符串？

Question

So I'm trying to test something out to see how rand() works in c++! I'm very new to c++ but I'm wondering how can I get the following code to print out either the letter B or A when the number 1 or 2 is generated?? the code ask if he wants to generate a letter, enter y for yes or n for no! then a letter generates but it seems to only generate the letter A?? any idea?

    #include <iostream>
    #include <ctime>
    #include <cstdlib>

    using namespace std;

    int main(){
        char x;
        char d;
        cout << "generate random letter?(y/n)" << endl;
        cin >> x;
        if (x = 'y'){
    srand(time(NULL));

    int randNum = (rand() % 2) + 1;
    if (randNum = 1){
        d = 'A';
    }
    else {
        d = 'B';
    }
    cout << d << endl;
}
else{ return 0; }
system("pause");
    }

Answer 1

Change this:

if (randNum == 1){

Answer 2

In modern C++, rand() is deprecated , and other techniques based on eg mt19937 Mersenne twister engine and uniform_int_distrubtion are used.

You may want to consider some code like this:

#include <iostream>     // For console output
#include <random>       // For pseudo-random number generators and distributions

int main()
{
    // Use random_device to generate a seed for Mersenne twister engine.
    std::random_device rd;    

    // Use Mersenne twister engine to generate pseudo-random numbers.
    std::mt19937 engine(rd());

    // "Filter" MT engine's output to generate pseudo-random integer values,
    // **uniformly distributed** on the closed interval [0, 1].  
    // (Note that the range is [inclusive, inclusive].)
    std::uniform_int_distribution<int> dist(0, 1);

    // Print 20 pseudo-random letters (A, B).
    for (int i = 0; i < 20; ++i)
    {
        // Generate pseudo-random number
        if (dist(engine) == 0)
        {
            std::cout << 'A';
        }
        else 
        {
            std::cout << 'B';
        }
        std::cout << ' ';
    }
    std::cout << std::endl;
}

Answer 3

When you say:

if(randNum = 1)

you assign the value 1 to randNum , then check if it is True . In C/C++ any non-zero number is True . In this way you always enter the first part of the if statement and get an 'A'.

Instead if you say:

if(randNum == 1)

you are comparing randNum to 1 and will get the behavior you want.

Answer 4

There's a much easier way to generate a random char. Chars can be created from an ASCII code number since we know from uppercase A to lowercase Z is in the range of 65-122 (google ASCII table)

std::random_device rd;
std::mt19937 engine(rd());
std::uniform_int_distribution<int> dist(65, 122);
char ascii_char = dist(engine);
std::cout << scii_char;

as a side note, std::uniform_int_distribution dist(65, 122) is inclusive, so it includes both 65 and 122.