Element in 2D Array Missing? - c

Question

I'm using function to assign the patterns of my 2D arrays. All the other arrays are displaying as it should except for my 'ans' array (the last row's dash is missing). Im guessing the problem is because of the 'pat2match' function (merges all the patterns). Because if i don's assign 'ans' to that 'function' and print an empty pattern array, all the dashes shows.
The function that merges the patterns:
char pat2match(char mypattern[13][13], char pat1[13][13], char pat2[13][13],
char pat3[13][13], char pat4[13][13], char pat5[13][13])
{
int r,c;
overlap(mypattern,pat5);
overlap(mypattern,pat2);
overlap(mypattern,pat4);
overlap(mypattern,pat3);
return overlap(mypattern,pat1);
}
Assigning the 'ans':
mytile(ans);
for(r=0;r<13;r++)
{
for(c=0;c<13;c++)
{
ans[r][c] = pat2match(ans,pattern1,pattern2,pattern3,pattern4,pattern5);
}
}
The overlap function:
char overlap(char pat1[13][13], char pat2[13][13])
{
int r,c;
for(r=0;r<13;r++)
{
//printf("|");
for(c=0;c<13;c++)
{
if(pat1[r][c] == ' ' || pat2[r][c] != ' ')
{
pat1[r][c] = pat2[r][c];
}
//printf(" %c ", pat1[r][c]);
}
//printf("|\n");
}
return pat1[r][c];
}
the empty pattern (the dash is like its border) :
void mytile(char pat[13][13])
{
int r,c;
for(r=0;r<13;r++)
{
for(c=0;c<13;c++)
{
if(r==0 || r==12)
{
pat[r][c] = '-';
}
else
{
pat[r][c] = ' ';
}
}
}
}

Answer 1

The return value from overlap is undefined behavior:
return pat1[r][c];
When this return statement is executed, both r and c are 13. Neither can be greater than 12. It is indexing past the bounds of the array, which is undefined behavior.