Program always producing same value?

Question

the point of my program is to write the numbers 1 - 1,000,000 to a text file, generate a random number between 1 and 1,000,000, search for that line in the text file, take the value, and square it (this is just an exercise for me, it has no practical application). The problem is that whenever I run it, the value remains the same, but the rand() function is seeded by time(0). I suspect that it's a garbage value but I don't know where it's coming from (I have no experience with GDB or any other standalone debuggers). Here's my source code:

#include <fstream>
#include <ctime>
#include <iostream>
#include <string>
#include <cstdlib>
using namespace std;

int main(int argc, char** argv){
    ofstream file("log.txt", ios::app);
    ofstream programLog("programlog.dat", ios::app);
    cout << "Test Start" << endl;
    programLog << "Test Start" << endl;
    cout << "Log file created" << endl;
    programLog << "Log file created" << endl;
    ifstream readFile("log.txt");
    int foundNum;
    std::string line = "";
    unsigned int loopCount = 1000000;
    unsigned int numToSearch;
    const unsigned short min = 1;
    const int max = 1000000;
    unsigned int randomLine = 0;

    for(int i = 0; i <= loopCount; i++){
        file << i << endl;
    }

    //select random line
    srand((unsigned)time(0));

    while(!(randomLine > min) && !(randomLine < max)){
        randomLine = (unsigned)rand();
        programLog << randomLine;
        int newlines = 0;
        //size_t found;
        while(getline(readFile, line)){
            if(line.find("\n") != string::npos)
                newlines++;
            if(newlines == randomLine)
                numToSearch = atoi(line.c_str());
        }

    }

    programLog << "Random line selected" << endl;

    //read line
    while(std::getline(readFile,line)){
        if(atoi(line.c_str()) == numToSearch){
            foundNum = numToSearch;
            break;
        }
        else
            continue;
    }

    //square it
    const unsigned int squared = foundNum*foundNum;

    programLog << squared;
    readFile.close(); //end read
    file.close(); //end log
    programLog.close(); //end programlog
    return 0;
}

`file << i << endl;` Rob's rule: Never say `endl` when you mean `'\n'`. See http://stackoverflow.com/questions/5492380/what-is-the-c-iostream-endl-fiasco/5492605#5492605 — Robᵩ, Sep 21 '11 at 02:03

score 2 · Accepted Answer · answered Sep 21 '11 at 01:51

You never enter the while loop as you are using:

while(!(randomLine > min) && !(randomLine < max))

while immediately evaluates to false. You should use:

while(randomLine < min || randomLine > max)

Also, why do all your variables have different types? This could lead to unintended errors. You should change them to have the same type.

score 1 · Answer 2 · answered Sep 21 '11 at 01:49

1

randomLineis initialized to 0, and still has that value once it reaches the while, so the loop body never executes.

answered Sep 21 '11 at 01:49

K-ballo

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Program always producing same value?

2 Answers2