C 字符串转数字

问题:给定一个字符串输入,将其转换为相应的数字

涉及知识点:字符串处理

分析:  1.输入字符串的合法性检查

          2.对于顺序读入的字符串,如何确定相应的权重

          3.处理非法字符串

          4.对于整数,小数,负数的处理

首先放上 C库函数中atoi函数的原型:

int ascii_to_int(char const *string){    int value;    value = 0;        while(*string <= '0'&&*string >= '9')    {        value *= 10;        value += *string - '0';        ++string;    }    if(*string != '0')        value = 0;        return value;}

这个原函数只对输入为数字字符的字符串进行处理,如果输入为非数字字符则不予处理,返回0

自己写的:

#include <stdio.h>#include <math.h>#include <stdbool.h>#define SIZE 500long double strToInt(char *str);char* dealWithStr(char *str);bool isNagetiveNumber(char *str);bool isPureDecimalNumber(char *str);bool isNagetive_PureDecimalNumber(char *str);int main(int argc, const char * argv[]){        char *orginal_Str;    char ch[SIZE];    printf("Please input the orginal string( Only numbers):\n");    scanf("%s",ch);    orginal_Str = ch;    char *checked_Str = dealWithStr(orginal_Str);        long double rs;    if (checked_Str != NULL) {        rs = strToInt(checked_Str);                printf("The int number of the string is %Lf\n",rs);    }else{            printf("Invalid input!\n");    }    return 0;}/***    将字符串转换为Int型整数 ***/long double strToInt(char *str){    long double result = 0;    long double resultForIntegerPart = 0;    long double resultForDecimalPart = 0;        int count = 0;    char *tempStr = str;        bool isNagetive = false;        bool isIntegerPart = true;    int countFordecimalPart = 0;    if (isNagetive_PureDecimalNumber(str) || isNagetiveNumber(str)) {        isNagetive = true;    }        /***        分析字符串,将其划分为整数和小数两个部分,分别计算     ***/while(*tempStr != '\0'){                switch (*tempStr) {            case '-':                tempStr++;                break;                            case '.':{                                isIntegerPart = false;                count = 0;                tempStr++;            }                break;            default:{                            int number = (int)(*tempStr - '0');                                /***                    整数部分                 ***/                if (isIntegerPart) {                    if(0 == count)                                                resultForIntegerPart += number;                    else{                                                resultForIntegerPart = resultForIntegerPart * 10 + number;                    }                    count++;                    tempStr++;                }else{                    /***                        小数部分                     ***/                    if(0 == count)                                                resultForDecimalPart += number;                    else{                                                resultForDecimalPart = resultForDecimalPart * 10 + number;                    }                    count++;                    countFordecimalPart++;                    tempStr++;                                    }            }                break;        }        }    /***        如果是整数部分     ***/    if (isIntegerPart) {        result = resultForIntegerPart;    }else{        result = resultForIntegerPart + resultForDecimalPart * pow(10,-countFordecimalPart);    }        if (isNagetive) {        result = result * -1;    }    return result;}/***    处理字符串,只允许输入数字字符串 ***/char* dealWithStr(char *str){    char *temp = str;    int countForMinus = 0;    int countForDecimalPoint = 0;            if (isNagetive_PureDecimalNumber(str)) {                countForDecimalPoint++;        countForMinus++;        temp += 2;    }else if (isNagetiveNumber(str)){                countForMinus++;;            temp++;    }else if(isPureDecimalNumber(str)){                countForDecimalPoint++;            temp++;    }    /***    允许输入数字,负号,小数点 ***/    while (*temp != '\0') {                if((*temp >= '0' && *temp<= '9') || *temp == '.') {            switch (*temp) {                case '.':                    countForDecimalPoint++;                    break;                default:                    break;            }            temp++;        }else{            break;        }    }        if ((countForDecimalPoint == 0 || countForDecimalPoint == 1) &&        (countForMinus == 0 || countForMinus == 1 ) && *temp == '\0')        return str;    else        return NULL;}/***    判断是否为负数 ***/bool isNagetiveNumber(char *str){    bool result = false;    char *temp = str;        if (*temp == '-') {        result = true;    }        return result;}/***    判断是否为纯小数 ***/bool isPureDecimalNumber(char *str){    bool result = false;    char *temp = str;        if (*temp == '.') {        result = true;    }            return result;}/***    判断是否为负纯小数 ***/bool isNagetive_PureDecimalNumber(char *str){    bool result = false;    char position_0 = *str;    str++;    char position_1 = *str;    if (position_0 == '-' && position_1 == '.') {        result = true;    }        return result;}