atoi 函数的实现

atoi()函数实现的功能是：将字符串转换为相应的整形；

atoi代码块的实现

#define _CRT_SECURE_NO_WARNINGS 1#include<iostream>using namespace std;//atoi()的实现(将字符串转为整形)int my_atoi(char * str){    int n=0;//保存整形      char firstChar = *str;//记录str的第一个字符    if (firstChar == '+' || firstChar == '-')//+123 -123    {        ++str;    }    while(*str == '0')//00123  -00123    {        ++str;    }    while (*str)    {        char temp = *str;        if (*str < '0' || *str> '9')        {            cout << "字符串不匹配" ;            return n;//该字符串含有非数字字符，不能转为整数        }        else        {            temp -= '0';            n = n * 10 + temp;//将字符串转为整形        }        str++;    }    if (firstChar == '-')    {        n = -n;    }    return n;}//测试代码块int main(){    char* str1 = "+123";    cout << "原字符串：" << str1 << "  ";    cout << "转换后整形：" << my_atoi(str1) <<endl;    char* str2 = "-123";    cout << "原字符串：" << str2 << "  ";    cout << "转换后整形：" << my_atoi(str2) << endl;    char* str3 = "-000123";    cout << "原字符串：" << str3 << "  ";    cout << "转换后整形：" << my_atoi(str3) << endl;    char* str4 = "+000123";    cout << "原字符串：" << str4 << "  ";    cout << "转换后整形：" << my_atoi(str4) << endl;    char* str5 = "1002300";    cout << "原字符串：" << str5 << "  ";    cout << "转换后整形：" << my_atoi(str5) << endl;    char* str6 = "12a3";    cout << "原字符串：" << str6 << "  ";    cout << "转换后整形：" << my_atoi(str6) << endl;    system("pause");    return 0;}

atoi 结果显示

itoa函数的实现