Fill 2d array random ints same number

Question

I'm trying to create a 2D array filled with random ints. The number of rows and columns are decided by the user. The issue is that when I run the program, the array is filled with the same number in each spot.

#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int** createArray(int rows, int cols){
// Create a 2D array of ints that is rows x cols
int** array = new int*[rows];
for(int i = 0;i<rows;++i){
 array[i] = new int[cols];
}
// Fill the array
srand(time(NULL));
for(int r = 0; r<rows; ++r){
 for(int c = 0;c<cols;++c){
 array[r][c] = (rand()%100);
 }
 }
return array;
}
int main(int argc, char* argv[]){
int** array;
int row = atoi(argv[1]);
int col = atoi(argv[2]);
array = createArray(row,col);
for(int x=0;x<row;x++){
 cout<<endl;
 for (int y=0;y<col;y++){
 cout<<array[row-1][col-1]<<" ";
 }
 }
cout<<endl;
return 0;
}

The output generally follows something along the lines of:

53 53 53
53 53 53
53 53 53

• Jarod42: [OT]: You have memleaks: you don't release array ('rows' and 'column').

Answer 1

The error is in your print loop, not your initialization.

 for(int x=0;x<row;x++){
 cout<<endl;
 for (int y=0;y<col;y++){
 cout<<array[row-1][col-1]<<" ";
 }
 }

That always prints the lower-right corner (row-1, col-1). You probably meant this:

 for(int x=0;x<row;x++){
 cout<<endl;
 for (int y=0;y<col;y++){
 cout<<array[x][y]<<" ";
 }
 }

Also a small usage tip: Don't call srand() in your createArray() function. If you call it anywhere, call it in main(), near the beginning, and make that the only place in your code it gets called.

• gainster: Thank you! Finals week left me a little brain dead X(

Answer 2

Your code has several errors:

1. The range in the print is wrong. It must be array[row][col]
2. Don't initialize srand() every time you call the function. It's a big mistake.
3. Don't use the modulo to get the random number. Multiply and divide: 100.0 * rand() / static_cast<double>(RAND_MAX)
4. Please! Free the memory you allocated. Call delete to free up the arrays you created (first free the internal arrays and finally the main array)

Answer 3

In your main row and cols arn't changing they are just the dimensions of your array. You have to print the values based on the corrdinates:

for(int x=0;x<row;x++){
 cout<<endl;
 for (int y=0;y<col;y++){
 cout<<array[x][y]<<" ";
 }
}
cout<<endl;

If you want to print the arry reversly you have to do this

for(int x=0;x<row;x++){
 cout<<endl;
 for (int y=0;y<col;y++){
 cout<<array[row-1-x][row-1-y]<<" "; // not row-1 and cols-1 as they're not changing
 }
}
cout<<endl;