Matrix Multiplication with Dynamically Allocated Arrays; Result Incorrect - c++

Question

I have been trying to debug this code for awhile, but I'm not sure how to actually access values in my IDE when they are located in dynamically allocated memory. This program is supposed to initialize two matrices based on the user's input and then multiply them together, if possible.
I have found a few mistakes and corrected them, but I'm not sure what is causing this issue.
#include <iostream>
using namespace std;
typedef int* IntArrayPtr;
int main() {
int r1, c1, r2, c2;
do {
//GET DIMENSIONS OF MATRICIES
cout << "Welcome! This program takes two matricies and multiplies them together.\n"
<< "Enter the number of rows and number of columns for Matrix 1: ";
cin >> r1 >> c1;
cout << "Enter the number of rows and number of columns for Matrix 2: ";
cin >> r2 >> c2;
//DETECT IF MULTIPLICATION CAN HAPPEN
if (r1 != c2) {
cout << "Error: matricies cannot be multiplied. Please enter a new set.\n";
}
} while (r1 != c2); //have the user enter again if the rows and columns don't match
cout << endl;
//INTIALIZE MATRICIES USING DYNAMIC ARRAYS
//intialize MATRIX 1
IntArrayPtr *a = new IntArrayPtr[r1];
cout << "For MATRIX 1: Enter the contained values. Press enter after each entry.\n";
for (int i = 0; i < r1; i++) {
a[i] = new int[c1]; //init columns for each row
cout << "ROW" << i + 1 << "\n";
for (int j = 0; j < c1; j++) {
cin >> a[i][j]; //fill columns of rows
}
cout << endl;
}
//intialize MATRIX 2
IntArrayPtr *b = new IntArrayPtr[r2]; //init rows
cout << "For MATRIX 2: Enter the contained values. Press enter after each entry.\n";
for (int i = 0; i < r2; i++) {
b[i] = new int[c2]; //intialize columns
cout << "ROW" << i + 1 << "\n";
for (int j = 0; j < c2; j++) {
cin >> b[i][j]; //fill columns of rows
}
cout << endl;
}
//INITIALIZE MATRIX TO STORE RESULT IN
//matrix will have the rows of the first and columns of the second, according to matrix multiplication
IntArrayPtr *c = new IntArrayPtr[r1]; //init rows
for (int i = 0; i < r1; i++) {
c[i] = new int[c2]; //init columns
}
//MULTIPLY MATRICIES
for (int i = 0; i < r1; ++i) {
for (int j = 0; j < c2; ++j) {
for (int k = 0; k < c1; ++k) {
c[i][j] += a[i][k] * b[k][j];
}
}
}
//PRINT RESULT
for (int i = 0; i < r1; i++) {
for (int j = 0; j < c2; j++) {
cout << c[i][j] << " ";
}
cout << endl;
}
delete[] a; delete[] b; delete[] c;
system("pause");
return 0;
}
The matrix should be the result of multiplication, but when I try to execute the program using small matricies (e.g. 3 x 2 times 2 x 3), the output spits out what seems to me to be garbage. I'm sure my mistake is silly, but help would be appreciated.

Answer 1

You didn't initialize the matrix c properly. Try this
//INITIALIZE MATRIX TO STORE RESULT IN
//matrix will have the rows of the first and columns of the second, according to matrix multiplication
IntArrayPtr *c = new IntArrayPtr[r1]; //init rows
for (int i = 0; i < r1; i++) {
c[i] = new int[c2]; //init columns
for (int j = 0; j < c2; j++) {
c[i][j] = 0;
}
}