C语言实现十六进制转换为十进制的方法详解

#include<stdio.h>
#include<string.h>
void conversion(char str[]){
    /**********  Begin  **********/
    int i=0,j=0,num=0,sum=0;
    int len=strlen(str);
 
    while(str[i]!='\0')
    {
        if(str[i]>='0'&&str[i]<='9')
           num=str[i]-'0';
        else if(str[i]>='a'&&str[i]<='f')
           num=str[i]-'a'+10;
        else if(str[i]>='A'&&str[i]<='F')
           num=str[i]-'A'+10; 
        else
           break;
        for(j=0;j<len-1;j++)
        {
            num=num*16;
        }
        sum+=num;   
        i++;
        len--;
    }
    printf("%d",sum);
    /**********  End  **********/
}

#include<stdio.h>
#include<string.h>
void conversion(char str[]) 
{
    /**********  Begin  **********/
    int i = 0, j=0,num = 0, sum = 0,len=0;
    //int len = strlen(str);//这种方法会将非16进制数记录在内
    while ((str[i] >= 'a' && str[i] <= 'f') || (str[i] >= 'A' && str[i] <= 'F') || (str[i] >= '0' && str[i] <= '9'))
    {
        len++;
        i++;
    } //遍历数组记录16进制数的个数，非16进制数不计在内 
    i = 0;
    while (str[i] != '\0')
    {
        //字符转数字
        if (str[i] >= '0' && str[i] <= '9')
            num = str[i] - '0';
        else if (str[i] >= 'a' && str[i] <= 'f')
            num = str[i] - 'a' + 10;
        else if (str[i] >= 'A' && str[i] <= 'F')
            num = str[i] - 'A' + 10;
        else
            break;//遇到'\0'之前的第一个非十六进制数就停止循环
        for (j = 0; j < len - 1; j++)
        {
            num = num * 16;
        }
        sum += num;
        i++;
        len--;//每读取一位就使长度-1
    }
    printf("%d\n", sum);
    /**********  End  **********/
}

#include<stdio.h>
#include<ctype.h>
int Get_0x(const char *str)
{
	int sum = 0;
	while(isspace(*str))
	{
		str++;
	}
	//此时 空格处理结束
	int index = 1;
	if(*str=='-' || *str=='+')
	{
		if(*str=='-')
		{
			index *= -1;
		}
		else
		{
			index = 1;
		}
		str++;
	}
	
	if((*str=='0') && (*(str+1)=='x'|| *(str+1)=='X'))
	{
		str+=2;
	}
	else
	{
		return INT_MAX;
	}
 
	while(isxdigit(*str))
	{
		if(isdigit(*str))
		{
			sum = sum*16 + (*str-'0'); 
		}
		else if(islower(*str))
		{
			sum = sum*16 + (*str-'a'+10);
		}
		else
		{
			sum = sum*16 + (*str-'A'+10);
		}
		str++;
	}
	if(*str == '\0')
		return sum * index;
	return INT_MAX;
}
int main()
{
	printf("%d\n", Get_0x("0x123ABcW"));
	printf("%d\n", Get_0x("0X123ABc"));
	printf("%d\n", Get_0x("      0x123ABc"));
	printf("%d\n", Get_0x("+0x123ABc"));
	printf("%d\n", Get_0x("-0x123ABc"));
	printf("%d\n", Get_0x("  +0x123ABc"));
	printf("%d\n", Get_0x("   -0x123ABc"));
    return 0;
}