NOIP I'm coming（写个快读练练手）

int readint(){
    int num=0;
    bool p=false;
    char c;
    c=cin.get();
    while((c<'0'||c>'9')&&c!='-')
        c=cin.get();
    if(c=='-')
        p=true;
    else
        num=c-'0';
    c=cin.get();
    while(c>='0'&&c<='9') {
        num=num*10+c-'0';
        c=cin.get();
    }
    if(p)
        return -num;
    return num;
}