谁来帮我看看……为什么会无效内存引用……

#include <stdio.h>
#include <string.h>
main()
{int n,r,i,j,m,l,k,x,y,z1,z2,z;
    char a[100][100],b[100][100]={"0"},c,d[5];
    scanf("%d\n",&n);
    for(i=0;i<n;i++)
    {   strcpy(a,b);
        scanf("%d ",&r);
            for(j=0;j<r;j++)
            {
                scanf("%s ",&a[j]);
                m=0;
                l=strlen(a[j]);
                while(1)
                {if(a[j][m]==48) m++;
                else break;
                }
                if(a[j][0]==48) {for(k=0;k<l-m+2;k++) a[j][k]=a[j][k+m-1];}
            }
            for(x=0;x<r-1;x++)
                    {for(y=x+1;y<r;y++)
                        {   z1=strlen(a[x]);
                            z2=strlen(a[y]);
                            if(z1<=z2) z=z2;
                            for(k=0;k<z;k++) {  if(a[x][k]>a[y][k]) break;
                                                if(a[x][k]<a[y][k]||(a[y][k]=="\0"||a[x][k]!="\0")) {strcpy(d,a[x]);
                             strcpy(a[x],a[y]);
                             strcpy(a[y],d);
                             break;}
           if(a[x][k]=="\0")  break;
                             }
                        }
                    }
        for(j=0;j<r;j++)
        printf("%s",a[j]);
        printf("\n");
    }
}