Visual Studio skipping multiple if statements? - c++

Question

I'm making a simple maze program that generates a maze. Currently I was working on making one and only solution to a maze, when I stumbled onto something weird. When I debug this code I see that VS is just skipping my if statements here:
for (i = 0; i <= (col * row) / 200; i++)
{
solution[se[0]][se[1]] = 1;
if (lab[se[0] + 1][se[1]]) se[0] + 1;
else if (lab[se[0]][se[1] + 1]) se[1] + 1;
else if (lab[se[0] - 1][se[1]]) se[0] - 1;
else if (lab[se[0]][se[1] - 1]) se[1] - 1;
solution[se[2]][se[3]] = 1;
if (lab[se[2] - 1][se[3]]) se[2] - 1;
else if (lab[se[2]][se[3] - 1]) se[3] - 1;
else if (lab[se[2] + 1][se[3]]) se[2] + 1;
else if (lab[se[2]][se[3] + 1]) se[3] + 1;
}
I hope it's not a duplicate, but I have no slightest idea what's the problem here, so it could be one.
Here's the full code if someone wants to replicate the problem:
#include <stdio.h>
#include <iostream>
#include <Windows.h>
#include <string>
CONSOLE_SCREEN_BUFFER_INFO csbi;
int **lab, **solution;
int col, row, i, j;
int main() {
GetConsoleScreenBufferInfo(GetStdHandle(STD_OUTPUT_HANDLE), &csbi);
col = csbi.srWindow.Right - csbi.srWindow.Left; row = csbi.srWindow.Bottom - csbi.srWindow.Top + 1; i = 0; j = 0;
lab = new int* [row];
for (i = 0; i < row; ++i)
lab[i] = new int[col];
solution = new int* [row];
for (i = 0; i < row; ++i)
solution[i] = new int[col];
for (i = 0; i < row; i++) { // Build basic maze
for (j = 0; j < col; j++) {
if (i == 0) lab[i][j] = 0;
else if (i == j == 1) lab[i][j] = 1;
else if (i == 1 && j == col - 1) lab[i][j] = 1;
else if (i == row - 1) lab[i][j] = 0;
else if (j == 0) lab[i][j] = 0;
else if (j == col - 1) lab[i][j] = 0;
else {
if (lab[i - 1][j] == 0) lab[i][j] = rand() % 2;
else {
if (lab[i - 1][j - 1] + lab[i - 1][j + 1] + lab[i - 2][j] <= 1) lab[i][j] = 1;
else {
lab[i][j] = rand() % 2;
}
}
}
}
}
int se[4] = { 1,1,1,col - 1 };
for (i = 0; i <= (col * row) / 200; i++) // Generate a solution
{
solution[se[0]][se[1]] = 1;
if (lab[se[0] + 1][se[1]]) se[0] + 1;
else if (lab[se[0]][se[1] + 1]) se[1] + 1;
else if (lab[se[0] - 1][se[1]]) se[0] - 1;
else if (lab[se[0]][se[1] - 1]) se[1] - 1;
solution[se[2]][se[3]] = 1;
if (lab[se[2] - 1][se[3]]) se[2] - 1;
else if (lab[se[2]][se[3] - 1]) se[3] - 1;
else if (lab[se[2] + 1][se[3]]) se[2] + 1;
else if (lab[se[2]][se[3] + 1]) se[3] + 1;
}
while (se[0] != se[2] || se[1] != se[3])
{
if (se[0] < se[2])
{
if (lab[se[2] - 1][se[3]]) se[2] - 1;
if (lab[se[0] + 1][se[1]]) se[0] + 1;
}
if (se[1] < se[3])
{
if (lab[se[2]][se[3] - 1]) se[3] + 1;
if (lab[se[0]][se[1] + 1]) se[1] + 1;
}
solution[se[0]][se[1]] = 1;
solution[se[2]][se[3]] = 1;
}
std::string out;
for (i = 0; i < row; i++) { // Print maze
for (j = 0; j < col; j++) {
if (solution[i][j]==1) out.append("#");
else if (!lab[i][j]) out.append("#");
else out.append(" ");;
}
std::cout << out << '\n';
out="";
}
system("pause");
for (i = 0; i < row; ++i) delete[] lab[i];
delete[] lab;
}
I'm sorry, this code is a mess, because it's still work in progress.
BTW I'm using VS 2019, didn't try it in another compiler yet. Is it really a compiler's fault?

Answer 1

The reason why the compiler sees fit to 'skip' the if blocks is because there is no code in them that has any effect!
For example, in the statement:
if (lab[se[0] + 1][se[1]]) se[0] + 1;
when the condition in the test is "true" what happens? The statement se[0] + 1 doesn't actually modify anything - it is simply an expression that has the given value.
What you probably want is to add 1 to se[0], so you need this:
if (lab[se[0] + 1][se[1]]) se[0] += 1;
and similarly for the other if and else if lines. (Note the added = character!)