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    C++

    Generate Random Numbers in C++ program

    Introduction

    In this post, we will discuss how to generate random numbers in C++ programs. C++ stdlib library provides us useful functions in generating random number sequences. rand() function when invoked returns a uniform random number from 0 to RAND_MAX interval.

    Code Listing

    Sample c++ program that generates 10 random numbers.

    /*******************************
    * Display 10 random numbers
    *******************************/
    #include<iostream>
    #include<stdlib.h>
    using namespace std;
    
    int main()
    {
     for(int i=0; i< 10; i++)
     {
     cout << rand() << endl;
     }
     return 0;
    }

     

    Program output:

    41
    18467
    6334
    26500
    19169
    15724
    11478
    29358
    26962
    24464

    Process returned 0 (0x0) execution time : 4.293 s
    Press any key to continue.

    Run the program another time and check the output. rand() function always produces the same random number sequence.

    srand()

    To produce different random numbers we can use srand() function.To this function you can set a seed value to produce different random numbers. seed should be different for each run of the program. For example, we can use current time as seed value. time(0) gives the current time. srand() expects the seed as unsigned int.

    /*******************************
    * Display 10 random numbers for
    * every run of the program.
    *******************************/
    #include<iostream>
    #include<stdlib.h>
    #include<time.h>
    using namespace std;
    
    int main()
    {
     srand((unsigned int) time(0));
     for(int i=0; i< 10; i++)
     {
     cout << rand() << endl;
     }
     return 0;
    }

    Run 1:

    9748
    27688
    3520
    32299
    23361
    28456
    20331
    17007
    14059
    5648

    Process returned 0 (0x0) execution time : 2.785 s
    Press any key to continue.

    *********************

    Run 2

    10150
    6254
    5357
    10199
    14102
    19924
    9947
    17400
    13369
    3099

    Process returned 0 (0x0) execution time : 0.450 s
    Press any key to continue.

    —

    The IDE used in the tutorial is Code:: Blocks. To download and install Code Blocks follow the link:

    https://www.testingdocs.com/download-and-install-codeblocks/

    For more information on Code Blocks IDE, visit the official website of Code blocks IDE:
    http://www.codeblocks.org/

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