Infinite while loop with a random number

Question

I have this code:

void generar() {

    while (true) {
        if (yPos == topOfTheWorld) {
            scene[xPos][yPos] = 2;
        } else if (yPos >= topOfTheWorld) {
            scene[xPos][yPos] = 1;
        } else if(yPos < topOfTheWorld) {
            scene[xPos][yPos] = 0;
        } else {
            scene[xPos][yPos] = 0;
        }

        yPos++;

        if(yPos>worldHeight) {
            topOfTheWorld += 0;
            yPos = 0;
            xPos++;
        }

        if (xPos>worldWidth) {
                    break;
        }
    }

std::ofstream output("mapa.txt");
    for(int y=0;y<worldHeight;y++) {
        for(int x=0;x<worldWidth;x++) {
            output<<scene[x][y];

            if(x<(worldWidth-1)){output<<",";}
        }
        if(y<(worldHeight-1)){output<<std::endl;}
    }

MessageBox(0, "World generation has finished!", "Finished!", MB_OK);

}

That generates a world based in an array. But when I add:

slope = random(5)-2;

To:

if(yPos == worldHeight) {
    topOfTheWorld += 0; //There would be the slope var...

if(yPos == worldHeight) {
    slope = random(5)-2;
    topOfTheWorld += slope;

For some reason the while becomes an infinite loop, and I don't know why.

(Random Function)

#include <time.h>
#include <windows.h>

int random(int n = 0) {

srand(time(NULL));

if(n!=0){
return rand() % n;
} else {
return rand();
}

}

(Variables)

const int worldWidth = 50;
const int worldHeight = 26;
int topOfTheWorld = worldHeight/2;
int xPos = 0;
int yPos = 0;
int scene[worldWidth][worldHeight];
int slope;

What can I do?

Answer 1

You show that scene is defined as:

int scene[worldWidth][worldHeight];

However, your code has this:

        if (xPos>worldWidth) {
                    break;
        }

Which means you will actually write a value outside the array boundary when xPos == worldWidth, and this causes undefined behavior. Adding the slope variable may cause your variable organization to change in a way that the undefined behavior ends up affecting the values of and or all of your loop control variables.

To fix, you should change the erroneous check with:

        if (xPos>=worldWidth) {
                    break;
        }

You have since edited your question with code that makes your yPos check incorrect in a similar way.

Answer 2

There's a repeated calls to srand in your random function

Fixes : -

void generar() {

srand(time(NULL)); //Remove srand() from random(), add it here
bool finished = false;

    while (!finished) {
        if (yPos == topOfTheWorld) {
            scene[xPos][yPos] = 2;
        } else if (yPos >= topOfTheWorld) {
            scene[xPos][yPos] = 1;
        } else if(yPos < topOfTheWorld) {
            scene[xPos][yPos] = 0;
        } else {
            scene[xPos][yPos] = 0;
        }

        yPos++;

        if(yPos == worldHeight) {
           // slope = random(5)-2; your random call
            topOfTheWorld += 0;
            yPos = 0;
            xPos++;
        }

        if (xPos>worldWidth) {
            finished = true;
           //goto Guardar; not required, 
          //also use of goto is bad programming practice
        }
    }