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Top Forums Programming generate array of random numbers Post 302595896 by saboture88 on Sunday 5th of February 2012 09:09:40 PM
Old 02-05-2012
generate array of random numbers

hi guys,
I am writing a c program that generates a two dimensional array to make matrix and a vector of random numbers and perform multiplication. I can't figure out whats wrong with my code. It generates a matrix of random numbers but all the numbers in the vector array is same and so is the result array. I don't see anything wrong with my multiplication algorithm but could anyone check it, please?

here is my code. help me figure out whats wrong with this
Code:
#include <iostream>
#include <cstdlib>
#include <time.h>

using namespace std;

const int mat_rows = 5;
const int mat_cols = 4;
const int vec_rows = mat_cols;
const int vec_cols = 0;

int matrix [mat_rows] [mat_cols];
int vector [vec_rows] [0];
int result [mat_rows] [0];
int res;

int main ()
{
srand (time(NULL));
/*Filling matrix with random value between 0 - 10 */
for (int i = 0; i < mat_rows; i++)
        for (int j = 0; j < mat_cols; j++)
                matrix [i][j] = rand () % 50;

/*Filling vector with random value between 0 - 10*/
for (int i = 0; i < vec_rows; i++)
        vector [i] [0]= rand () % 50;

cout << "Printing out the matrix" << "\n" << endl;
for (int i = 0; i < mat_rows; i++)
        {
        for (int j = 0; j < mat_cols; j++)
                cout << matrix [i][j] << "   ";
        cout << endl;
        }
cout << "Printing out the vector" << "\n" << endl;
for (int i = 0; i < vec_rows; i++)
        cout << vector [i] [0] << endl;

for (int i = 0; i < mat_rows; i++)
        {
        res = 0;
        int vrows = 0;
        for (int j = 0; j < mat_cols; j++)
                {
                res = res + ((matrix [i] [j]) * (vector [vrows] [0]));
                vrows++;
                }
        result [i] [0] = res;
        }

for (int i = 0; i < mat_rows; i++)
        cout << result [i] [0] << endl;

return 0;
}

thanks
 

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rand(3UCB)					     SunOS/BSD Compatibility Library Functions						rand(3UCB)

NAME
rand, srand - simple random number generator SYNOPSIS
/usr/ucb/cc[ flag ... ] file ... int rand() int srand( seed); unsigned seed; DESCRIPTION
rand() uses a multiplicative congruential random number generator with period 2**32 to return successive pseudo-random numbers in the range from 0 to "2**31 -1." srand() can be called at any time to reset the random-number generator to a random starting point. The generator is initially seeded with a value of 1. SEE ALSO
drand48(3C), rand(3C), random(3C) NOTES
Use of these interfaces should be restricted to only applications written on BSD platforms. Use of these interfaces with any of the system libraries or in multi-thread applications is unsupported. The spectral properties of rand() leave a great deal to be desired. drand48(3C) and random(3C) provide much better, though more elaborate, random-number generators. The low bits of the numbers generated are not very random; use the middle bits. In particular the lowest bit alternates between 0 and 1. SunOS 5.10 12 Feb 1993 rand(3UCB)
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