Question

I basically, for this assignment, have to make a mini-program that randomly generates a string of letters based on randomized numbers (for which 0 corresponds to A, 1 corresponds to B, 2 corresponds to C, and so on) alongside with a number n corresponding to the nth string generated. These strings and their corresponding numbering are to be printed out to a text file. For example, if my function was called myFunction:

myFunction("file.txt", 3)

Produces a text file called “file.txt” with the following contents:

AAAAAAAA 1
IWFNWEFS 2
WEWEFCSD 3

Where the strings’ letters are each supposed to be randomized.

However, for some reason each of my strings are identical for some reason. That is, for each row of string-number pairs, all the strings turn out to be the same (when I am supposed to make them all different/random). Why is this happening? Here is my code:

#include <iostream>
#include <vector>
#include <cstdlib>
#include "math.h"
#include <fstream>
using namespace std;

string key = ""; // Empty initial key for use in "makeKey".

// "makeKey" function to create an alphabetical key 
// based on 8 randomized numbers 0 - 25.
void makeKey() {
    int k;
    for (k = 0; k < 8; k++) {
        int keyNumber = (rand() % 25);
        if (keyNumber == 0)
            key.append("A");
        if (keyNumber == 1)
            key.append("B");
        if (keyNumber == 2)
            key.append("C");
        if (keyNumber == 3)
            key.append("D");
        if (keyNumber == 4)
            key.append("E");
        if (keyNumber == 5)
            key.append("F");
        if (keyNumber == 6)
            key.append("G");
        if (keyNumber == 7)
            key.append("H");
        if (keyNumber == 8)
            key.append("I");
        if (keyNumber == 9)
            key.append("J");
        if (keyNumber == 10)
            key.append("K");
        if (keyNumber == 11)
            key.append("L");
        if (keyNumber == 12)
            key.append("M");
        if (keyNumber == 13)
            key.append("N");
        if (keyNumber == 14)
            key.append("O");
        if (keyNumber == 15)
            key.append("P");
        if (keyNumber == 16)
            key.append("Q");
        if (keyNumber == 17)
            key.append("R");
        if (keyNumber == 18)
            key.append("S");
        if (keyNumber == 19)
            key.append("T");
        if (keyNumber == 20)
            key.append("U");
        if (keyNumber == 21)
            key.append("V");
        if (keyNumber == 22)
            key.append("W");
        if (keyNumber == 23)
            key.append("X");
        if (keyNumber == 24)
            key.append("Y");
        if (keyNumber == 25)
            key.append("Z");
    }
    return;
}

// "makeFile" function to produce the desired text file.
// Note this only works as intended if you include the ".txt" extension,
// and that a file of the same name doesn't already exist.
void makeFile(string fileName, int n) {
    ofstream ourFile;
    ourFile.open(fileName);
    int k; // For use in below loop to compare with n.
    int l; // For use in the loop inside the below loop.
    for (k = 1; k <= n; k++) {
        for (l = 0; l < 8; l++) {  // To write to the file ONE key
        ourFile << key[l];         // C++ only lets me do it this way...
        }
        ourFile << "  " << k << "\n"; // Writes two spaces and the data value
    }
}

// Primary function to create our desired file!
void mainFunction(string fileName, int n) {
    makeKey();
    makeFile(fileName, n);
}

int main() {
    mainFunction("file.txt", 3); // To test program
    cin.get();
    return 0;
}

I tried using both srand ( time(NULL) ); and srand (1); in the first part, but that didn’t work for me either.

Answer 1

Each time you call makeKey, it appends 8 more characters to the end of key, but you never clear out the previous contents, and after calling makeKey, you print out the first 8 characters, which haven’t changed.

I’d get rid of the global variable key, and have makeKey return a (newly created) std::string every time it’s called.

FWIW, I’d also rewrite makeKey to convert from numbers to letters by indexing into an array of char.

Edit (In response to the edit in the question): Yes, you probably also want to use srand(time(NULL)); at the beginning of the program. srand(1); is the same as if you didn’t bother to call srand at all. Using srand(time(NULL)); should normally give a different sequence of results every time you run the program (unless you run it twice so quickly that the system clock doesn’t change in between — normally twice in the same second).

Right now you’re getting one string repeated 8 times. Fixing the problem noted above will give you 8 different strings — but without something like srand(time(NULL));, you’ll get the same group of 8 strings ever time you run the program. If you just add srand(time(NULL)); and don’t fix the rest, you’ll get one string 8 times, but it’ll be a different one each time you run the program (whereas right now, even the one string you get will be the same as every other time you run the program).