include <stdio.h>main(){char *s="12134211";int v[4]={0,0,0,0},k,i;for (k=0;s[k];k++){switch(s[k]){case'1':i=0;case'2':i=1;case'3':i=2;case'4':i=3;}v[i]++;}for(k=0;k<4;k++)printf("%d",v[k]);}怎么看