这段代码一次执行良好，另一次出现分段错误

Question

I have gems objects gems[10][10], which have an attribute color. I want to get three or more consecutive gems in a column having same color, and change thier color. The code below works just fine once while gives segmentation fault the other time. What cause the segmentation fault in random runs.

    bool findMatch(){
        for(int i=0;i<10;++i){      // To check ForVertical matchces
            for(int j=1;j<10;++j){
                int count=0;
                int a=0;
                if(gems[j][i].getColor()==gems[j-1][i].getColor()){
                    a=j;
                    count++;
                    while(gems[a][i].getColor()==gems[j][i].getColor() && a<10){
                        count++;
                        a++;
                    }
                }
             if(count>=3){
                 for(int x=j-1, itr=0;itr<count;++itr,++x){
                     gems[x][i].setColor(7);
                 }
                    glutPostRedisplay();
                 for(int x=j-1, itr=0;itr<count;++x,++loop){
                     gems[x][i].setColor(GetRandInRange(0,7));
                 };
                 return true;
             }
            }
        }
return false;
}

Answer 1

 while(gems[a][i].getColor()==gems[j][i].getColor() && a<10){

When a reaches the value of 10, here. gems[10] gets evaluated before the a<10 comparison. Since this exceeds the size of the array, this results in undefined behavior.