Basics of rand() in C++ & its Application.

 Basics of rand()

The rand() function in C++ generated a random value in the 'int' acceptable values. This can be used in multiple cases that helps optimize our code for a better result.

Let us start by learning the basic syntax and how we can manipulate the rand() function to generate a value which we would prefer to see more often.

#include<bits/stdc++.h>

using namespace std;

int main()

{

    //syntax of rand() function

        cout<<rand()<<endl;

        

    //max value of rand() function

        cout<<RAND_MAX<<endl;

        

    //trends with 'int' data type

        cout<<INT_MAX<<endl;

        

    //controlling rand() values

    

        //between 0-9 (inclusive)

        cout<<rand()%10<<endl;

        

        //between 0-99 (inclusive)

        cout<<rand()%100<<endl;

        

    //generate at max 100 values

    //each value being at max 10000

    cout<<endl;

    int n=rand()%100;

    for(int i=0;i<n;i++)

    {

        cout<<rand()%10000<<endl;

    }

}

Now, the application of rand() begin from testing to optimizing to fault tolerance and exception handling.

We can generate a function which would give us test cases for our code. Then we can run it and see of we get a desired output. If we get hit with some error, we will then know for which test cases our code gives this issue.

Let us see this from a bank's perspective. We have 3 variables, exist, deposit and withdraw. Obviously for any test case

if 

    exist + deposit < withdraw

then it should throw an error.

Here is a code which is explained in the shorts.

#include<bits/stdc++.h>

using namespace std;

int generate(int exist,int deposit,int withdraw)

{

    //making test cases

    if(exist==-1)

    {

        exist=rand();

        return exist;

    }

    

    else if(deposit==-1)

    {

        deposit=rand();

        return deposit;

    }

    

    else

    {

        withdraw=rand();

        return withdraw;

    }

}

int condition_checker(int exist,int deposit,int withdraw)

{

    //you can withdraw from new exist value

    exist+=deposit;

    

    //failed condition

    if(exist<withdraw)

        cout<<"'withdraw' too big"<<endl;

    

    else

        cout<<exist-withdraw<<endl;\

        

    return 0;

}

int bank_return()

{

    //the values initialised for condition passing

    int exist=-1, deposit=-1, withdraw=-1, n=0;

    

    //only if n between 1000 & 10000

    //the loop will be exited

    while(n<1000)

    {

        n=rand()%10000;

    }

    

    //generate test values for variables 'n' times

    for(int i=0;i<n;i++)

    {

        exist = generate(exist,0,0);

        deposit = generate(0,deposit,0);

        withdraw = generate(0,0,withdraw);

        

        //to see how the tested values perform

        condition_checker(exist,deposit,withdraw);

    }

    return 0;

}

int main()

{

    //magic area

    bank_return();

}

Here is a sample output.