字符串中最长的数字串

返回一个以“\0”结束的字符串中提取最长的数字串

不能使用任何库函数或已经存在的函数，如strlen

#include <stdio.h>#include <stdlib.h>char* maxnum(char *source){    char *a = source,*temp,*dest;    int maxlen = 0,len = 0;        while(*a++){        if(*a >= '0' && *a <= '9')            len++;        else{            if(len > maxlen){             maxlen = len;                temp = a - maxlen;            }            len = 0;        }    }    dest = (char*)malloc(maxlen * sizeof(char));    for(len = 0;len < maxlen;len++)    dest[len] = temp[len];    dest[len] = '\0';    return dest;}void main(){    char a[] = "abdf16723sdgdfjo12j423m534s588886",*b;        b = maxnum(a);        printf("%s\n",b);}