Question

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define SIZE 8
#define POP 8

int answers[SIZE] = {5,3,1,7,4,6,0,2};

int getRand(int mod){
    if (mod==0) return 0;
    else return random()%mod;
}

void printArray(int array[]){
    int i;
    for(i=0; i<SIZE-1; i++) printf("(%i,%i),",i,array[i]);
    printf("(%i,%i)",SIZE-1,array[SIZE-1]);
    printf("\n");
}

int getWeight(int array[]){
    int weight = 28;
    int queen;
    for(queen=0;queen<SIZE;queen++){ //for each queen
        int nextqueen;
        for(nextqueen=queen+1;nextqueen<SIZE;nextqueen++){ //for each of the other queens (nextqueen = queen to avoid counting pairs twice)
            if(array[queen] == array[nextqueen] || abs(queen-nextqueen)==abs(array[queen]-array[nextqueen])){ //if conflict
                weight--;
            }
        }
    }
    return weight;
}

void geneticAlgorithm(){
    int population[POP][SIZE];
    int children[POP][SIZE];
    int weightProb[] = {};
    int wpl = 0; //weightProb[] length
    float mutProb = 0.05;
    int done = 0;
    int i;
    for(i=0;i<POP;i++) for(int j=0;j<SIZE;j++) population[i][j] = getRand(SIZE);
    while(done == 0){
        for(i=0;i<POP;i++){
            if(getWeight(children[i]) == 28){
                printf("solution: ");
                printArray(children[i]);
                done = 1;
            }
        }

        for(i=0;i<wpl;i++) weightProb[i] = (int)NULL; //clear weightprob
        wpl=0;

        //weighted probability distribution
        for(i=0;i<POP;i++){
            int w = getWeight(population[i]);
            for(int j=0;j<w;j++){
                weightProb[wpl] = i; //fill array with member number w times
                wpl++;
            }
        }

        //reproduce
        for(i=0;i<POP;i+=2){
            int par1 = weightProb[getRand(wpl)];
            int par2 = weightProb[getRand(wpl)];
            int split = getRand(SIZE);
            //crossover
            for(int j=0;j<split;j++){
                children[i][j] = population[par1][j];
                children[i+1][j] = population[par2][j];
            }
            for(int j=split;j<SIZE;j++){
                children[i][j] = population[par2][j];
                children[i+1][j] = population[par1][j];
            }
            //mutation
            if(getRand(1000000)<=mutProb*1000000){
                int child=getRand(2);
                if(child == 0) children[i][getRand(SIZE)] = getRand(SIZE);
                else children[i+1][getRand(SIZE)] = getRand(SIZE);
            }
        }
        for(i=0;i<POP;i++) for(int j=0;j<SIZE;j++) population[i][j] = children[i][j];
        wpl = 0;
    }
}

int main(int argc, const char * argv[]){
    srandom((unsigned int)time(NULL)); //seed random
    geneticAlgorithm();
    return 0;
}

when filling weightProb[], the population randomly changes.
i’ve debugged using print statements and it stops when wpl++ is commented out, but that is required
(wpl is the length of the weightProb array).
how is this happening?

Answer 1

This declaration:

int weightProb[] = {};

declares an empty array. This means each time you write to an element you write out of bounds of the array, and bad things will happen.