利用sscanf取数，进行数字范围是否正确判断，与数字个数是否正确判断。

#include <stdio.h>
#include <string.h>
int f2(char *IP){
    int n=strlen(IP);
    int num[4]={-1};
    sscanf(IP,"%d.%d.%d.%d",&num[0],&num[1],&num[2],&num[3]);
    int count[4]={0};
    char recode[4][3]={0};
    for(int i=0;i<4;i++){
        if(num[i]>=0&&num[i]<=255){
            int temp=num[i];
            if(temp==0){
                count[i]=1;
                recode[i][0]='0';
            }else{
                while(temp>0){
                 //recode[i][count[i]]=temp%10+'0';
                 count[i]++;
                 temp=temp/10;
                }
            }
        
        }else{return 0;}
    }
    int sum=0;
    for(int i=0;i<4;i++){
        //if(memcmp(&IP[sum],recode[i],count[i]*sizeof(char))!=0){return recode[i+1][0]-'0'+10;}
        sum+=count[i]+1;
    }
    if(sum-1!=n){return 0;}
    return 1;
}
int main(){
    char str[20]={0};
    while(~scanf("%s",str)){
         //printf("%d ",f2(str));
        if(f2(str)){
            printf("YES\n");
        }else{printf("NO\n");}
}
    
}