输入一段字符，求里面字母，数字，空格，和其他字符；运行不了，看不出问题 求解

Question

#include<stdio.h>int main(){ int i,a=0,b=0,c=0,d=0,e,f;char s1[i]; scanf("%s",&s1[i]);gets(s1);for(i=0;s1[i]!='/0';i++){if('A'<=s1[i]&&s1[i]<='Z'||'a'<=s1[i]&&s1[i]<='z'){a=a++;}if('0'<=s1[i]<='9'){b=b++;}if(s1[i]==' '){c=c++;}}printf("%d %d %d",a,b,c); }