C语言 这个表达式怎么理解 新手请大神详述total += isalnum(ch[i])!=0;

C语言 这个表达式怎么理解 新手请大神详述total += isalnum(ch[i])!=0;
#include "stdio.h"
#include "ctype.h"
main()
{
\x05char ch[40];
\x05int i = 0;
\x05int alpha = 0;
\x05int digit = 0;
\x05int total = 0;
\x05printf("请输入字符串：\n");
\x05fgets(ch,sizeof(ch),stdin);
\x05while (ch[i]!='\0')
\x05{
\x05\x05total += isalnum(ch[i])!=0;
\x05\x05digit += isdigit(ch[i])!=0;
\x05\x05alpha += isalpha(ch[i])!=0;
\x05\x05i++;
\x05}
\x05printf("数字：%d\n",digit);
\x05printf("字母：%d\n",alpha);
\x05printf("总共：%d\n",total);
}