atoi函数编写

#include<iostream>
#include<string>
using namespace std;
int ai(const char *p){
	bool negflag = false;
	int rs = 0;
	if(*p=='+'||*p=='-'){
		negflag=(*p=='-');
		p++;
	}
	while(isdigit(*p)){
		rs=rs*10+(*p-'0');
		p++;
	}
	if(negflag) rs=0-rs;
	return rs;
}
void main(){
	const char a[] ="123";
	int k;
	k=ai(a);
	cout<<k;
	system("pause");
}