dynamic arrays c++ Access violation writing location - dynamic-arrays

Question

What is wrong with my code ? I have the error like this.
Unhandled exception at 0x00d21673 in mnozenie_macierzy.exe : 0xC0000005: Access violation writing location 0xcdcdcdcd.
It create the first array and the half to the second. The program multiplies arrays.
Sorry for my English if It isn't correct. I hope you understand me.
#include <iostream>
#include <time.h>
using namespace std;
void losowa_tablica(int **tab1, int **tab2, int a, int b, int c, int d)
{
int i, j;
for(i=0; i<a; i++)
{
cout << endl;
for(j=0; j<b; j++)
{
tab1[i][j]=rand();
cout << "tab1[" << i << "][" << j << "] : \t" << tab1[i][j] << "\t";
}
}
cout << endl;
for(i=0; i<c; i++)
{
cout << endl;
for(j=0; j<d; j++)
{
tab2[i][j]=rand();
cout << "tab2[" << i << "][" << j << "] : \t" << tab2[i][j] << "\t";
}
}
cout << endl << endl;
}
int **mnozenie(int **tab1, int **tab2, int a, int b, int c, int d)
{
int g, suma, i, j;
int **mac=new int*[a];
for(int i=0; i<d; i++)
mac[i]=new int[d];
for(i=0; i<a; i++)
for(j=0; j<d; j++)
{
g=b-1, suma=0;
do
{
suma+=tab1[i][g]*tab2[g][j];
g--;
}while(g!=0);
mac[i][j]=suma;
}
return mac;
}
int main()
{
int a,b,c,d;
cout << "Podaj liczbe wierszy pierwszej macierzy: " << endl;
cin >> a;
cout << "Podaj liczbe kolumn pierwszej macierzy: " << endl;
cin >> b;
cout << "Podaj liczbe wierszy drugiej macierzy: " << endl;
cin >> c;
cout << "Podaj liczbe kolumn drugiej macierzy: " << endl;
cin >> d;
int **tab1=new int*[a];
for(int i=0; i<b; i++)
tab1[i]=new int[b];
int **tab2=new int*[c];
for(int i=0; i<d; i++)
tab2[i]=new int[d];
losowa_tablica(tab1, tab2, a, b, c, d);
if ( b==c )
{
cout << "Mnozenie wykonalne" << endl;
int **mno=mnozenie(tab1, tab2, a, b, c, d);
}
else cout << "Mnozenie niewykonalne" << endl;
system("pause");
}

Answer 1

Your code yields undefined behavior:
int **tab1=new int*[a]; // allocating an array of 'a' elements
for(int i=0; i<b; i++) // if b > a then the next line will eventually yield UB
tab1[i]=new int[b];
int **tab2=new int*[c]; // allocating an array of 'c' elements
for(int i=0; i<d; i++) // if d > c then the next line will eventually yield UB
tab2[i]=new int[d];
int **mac=new int*[a]; // allocating an array of 'a' elements
for(int i=0; i<d; i++) // if d > a then the next line will eventually yield UB
mac[i]=new int[d];
In practice, the above code will most likely perform a memory access violation at some point.