Strange occurence in genetic algorithm implementation - c

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.