重力计算导致NaN.没有明确的理由

我的猜测是分裂出了问题.我已经分析了很多案例,但仍然找不到导致值为NaN的出现模式.

这是我的代码：

#include <stdio.h>
#include <math.h>
#include <time.h>
#include <stdlib.h>

double G;  
int N;
int T;
int COUNT;

typedef struct 
{
    double rx,ry;
    double vx,vy;
    double fx,fy;
    double mass;
} Body;

void updateBody (Body* bodyInstance,int timestamp) {
    bodyInstance->vx += timestamp * bodyInstance->fx / bodyInstance->mass;
    bodyInstance->vy += timestamp * bodyInstance->fy / bodyInstance->mass;
    bodyInstance->rx += timestamp * bodyInstance->vx;
    bodyInstance->ry += timestamp * bodyInstance->vy;
};

void updateBodyForces (Body* bodyA,Body* bodyB) {
    double dx,dy,dist,force;
    dx = bodyB->rx - bodyA->rx;
    dy = bodyB->rx - bodyA->rx;
    // collision/same place in spacetime hack
    if (bodyB->rx == bodyA->rx && bodyB->ry == bodyA->ry) {
        dist = 1;
    } else {
        dist = sqrt(pow(dx,2) + pow(dy,2));
    }
    force = (G * bodyA->mass * bodyB->mass) / (pow(dist,2) + 100);
    bodyA->fx += force * dx / dist;
    bodyA->fy += force * dy / dist;
}

void resetBodyForces (Body* bodyInstance) {
    bodyInstance->fx = 0;
    bodyInstance->fy = 0;
}

void getRandomBody (Body* bI) {
    bI->rx = rand() % 10;
    bI->ry = rand() % 10;
    bI->vx = rand() % 10;
    bI->vy = rand() % 10;
    bI->fx = 0;
    bI->fy = 0;
    bI->mass = 20;
}

int main( int argc,char *argv[] )  {
    G = argc >= 2 ? atof(argv[1]) : 0.01;  
    N = argc >= 3 ? atoi(argv[2]) : 3;
    T = argc >= 4 ? atoi(argv[3]) : 1;
    COUNT = argc >= 5 ? atoi(argv[4]) : 10;
    srand(time(NULL));
    Body bodies[N];
    for (int i=0; i<N; i++) {
        getRandomBody(&bodies[i]);
    }
    for (int i = 0; i < COUNT; i++) {
        for (int j = 0; j < N; j++) {
            resetBodyForces(&bodies[j]);
            for (int k = 0; k < N; k++) {
                if (j != k) {
                    updateBodyForces(&bodies[j],&bodies[k]);
                }
            }
        }
        for (int j = 0; j < N; j++) {
            updateBody(&bodies[j],T);
        }
    }
}