十六进制转十进制 谭浩强教材课后习题

#include<stdio.h>

size_t HextoDec(char s[])
{
    size_t i, n;
    n = 0;
    for (i = 0; s[i] != '\0'; i++)
    {
        if (s[i] >= '0'&& s[i] <= '9')
            n = n * 16 + s[i] - '0';
        if (s[i] >= 'a' && s[i] <= 'f')
            n = n * 16 + s[i] - 'a' + 10;
        if (s[i] >= 'A' && s[i] <= 'F')
            n = n * 16 + s[i] - 'A' + 10;
    }
    return n;
}

int main()
{
    size_t result = 0;
    char hex[9] = {0}; 
    printf("input a HEX number:");
    scanf("%s", hex);

    result = HextoDec(hex);
    printf("0x%s = %u\n", hex, result);
    
    return 0;
}

转自博客https://blog.csdn.net/gjggj/article/details/92415602

 

 

 

略微注释

#include<stdio.h>

int HextoDec(char s[])
{
    int i,n;
    n=0;//n为最后结果 
    for (i=0;s[i]!='\0';i++)//设置循环来读取数组中的数，每一次循环最高位的数的位权都会加1（最高位为第一位） 
    {
        if (s[i]>='0'&&s[i]<='9')
            n=n*16+s[i]-'0';//减去0字符的ascii码来达到同步 
        if (s[i] >= 'a' && s[i]<='f')//大小写一致 
            n=n*16+s[i]-'a'+10;
        if (s[i]>='A'&&s[i]<='F')
            n=n*16+s[i]-'A'+10;
    }
    return n;
}
int main()
{
    int result=0;
    char hex[9]={0}; 
    printf("输入一个十六进制数:");
    scanf("%s", hex);

    result=HextoDec(hex);
    printf("0x%s = %u\n",hex,result);
    
    return 0;
}