Input a matrix in c++? - c++

Question

I'm just a beginner of C++ and I want to write a program which inputs and then displays a matrix of order i * j. I have written the following program but it did not work.
Kindly guide me .
I think may be the method of accessing is not right or something like that.
Here is the program:
#include <iostream>
using namespace std;
int main() {
int i = 0,j = 0;
cout << "Enter no of rows of the matrix";
cin >> i;
cout << "Enter no of columns of the matrix";
cin >> j;
float l[i][j];
int p = 0, q = 0;
while (p < i) {
while (q < j) {
cout << "Enter the" << p + 1 << "*" << q + 1 << "entry";
cin >> l[p][q];
q = q + 1;
}
p = p + 1;
q = 0;
}
cout << l;
}

Answer 1

you cant define an array with variable length. You need to define a dynamic arrays or std::vector
#include<vector>
std::vector<std::vector<int> > l(i, std::vector<int>(j, 0));
And cout << l will only print out the value of a int** . To print out each individual integer, you need to loop against each of them.
for(int x = 0; x < i; ++i){
for(int y = 0; y < j; ++y){
cout << l[x][y] << " "
}
cout << "\n";
}

Answer 2

I rewrote your code:
(instead of alloc its better to use new in c++, and use delete to free the memory)
#include "stdafx.h"
#include<iostream>
#include <conio.h>
using namespace std;
int _tmain()
{
int row,col;
cout<<"Enter no of rows of the matrix";
cin>>row;
cout<<"Enter no of columns of the matrix";
cin>>col;
float** matrix = new float*[row];
for(int i = 0; i < row; ++i)
matrix[i] = new float[col];
int p=0,q=0;
for(unsigned i=0;i<row;i++) {
for(unsigned j=0;j<col;j++) {
cout<<"Enter the"<<i+1<<"*"<<j+1<<"entry";
cin>>matrix[i][j];
}
}
for(unsigned i=0;i<row;i++) {
for(unsigned j=0;j<col;j++) {
cout<<matrix[i][j]<<"\t";
}
cout<<endl;
}
getch();
return 0;
}