Hexadecimal to decimal-C

We often encounter a situation where the hexadecimal number is converted to the hexadecimal number. We can use the following C program to complete the above work.

How does it work?

6.2.5 convert the hexadecimal number to the decimal number. The hexadecimal value is 16 to 1, but we only have 0 ~ 9. Therefore, we use the letters A, B, C, D, E, and F to represent 10, 11, 12, 13, 14, and 15 respectively. Uppercase letters are not case sensitive. The 0th bits in hexadecimal notation are 0 to the power of 16, 1st bits are 1 to the power of 16, and 2nd bits are 2 to the power of 16 ...... Therefore, in the Nth (N starts from 0) bit, if it is a number X (X is greater than or equal to 0, and X is less than or equal to 15, that is, F) it indicates the N power of X * 16. Suppose there is a hexadecimal number 2AF5, how can we convert it into a hexadecimal number? Convert 2AF5 to 10 hexadecimal: 0th bits: 5*160 = 5 1st bits: F * 161 = 240 2nd bits: A * 162 = 2560 3rd bits: 2*163 = 8192 + ----------------------------------- 10997 direct calculation is: (5*160) + (F * 161) + (A * 162) + (2*163) = 10997 (don't forget, in the above calculation, A indicates 10, and F indicates 15)

Note *

In this way, the program requires two components:

1. Weight Calculation

Power (16, x)

unsigned long power(int a, int b){  int i;  unsigned long result = 1;  for(i = 0; i < b; i++)  {    result *= a;  }  return result;};

2. convert a single hexadecimal value to a decimal Value

For example, if it is F, it indicates 15

   switch (ch)    {  case '0':iCh = 0;break;  case '1':iCh = 1;break;  case '2':iCh = 2;break;  case '3':iCh = 3;break;  case '4':iCh = 4;break;  case '5':iCh = 5;break;  case '6':iCh = 6;break;  case '7':iCh = 7;break;  case '8':iCh = 8;break;  case '9':iCh = 9;break;  case 'a':iCh = 10;break;  case 'b':   iCh = 11;break;  case 'c':  iCh = 12;break;  case 'd':  iCh = 13;break;  case 'e':  iCh = 14;break;  case 'f':  iCh = 15;break;  default:iCh = -1;break;  }

To meet the requirements, you can use the system function tolower () or our own function toLower () to convert all input to lowercase letters ()

int toLower(int c){  if(c >= 'A' && c <= 'Z')  {     return c + 'a' - 'A';  } else {     return c;  }};

The complete procedure is as follows:

/* * hex2int.c * *  Created on: 2010-07-20 *      Author: xiaobin * */#include 
 
  /* #include 
  
    */#include 
   
    //#include 
    
     /* int max is 32767 *//* "%d" only print int *//* long max is 2147483647 *//* "%ld" can print long type *//* unsigned long max is 4294967295 *//* "%lu" can print unsigned long type */#define MB 0x0100000ULunsigned long power(int a, int b);int toLower(int c);unsigned long htoi(char s[]);int main(int argc, char* argv[]){    if(argc > 1)        printf("long integer: %lu\n", htoi(argv[1]));    printf("M/Byte: %ld\n", MB);    return 0;}unsigned long htoi(char *s){    int i, len;    unsigned long value, result;    int iCh;    unsigned long iPow;    int pos;    char ch;    result = 0;    len = 0;    value = 0;    iCh = -1;    len = strlen(s);    pos = 0;    len -= 1;    for(i = len; (s[i] >= '0' && s[i] <= '9')                    || (s[i] >= 'a' && s[i] <= 'f')                    || (s[i] >= 'A' && s[i] <= 'F'); i--) {        ch = toLower(s[i]); /* tolower() defined in ctype.h */        switch (ch) {          case '0':            iCh = 0;            break;          case '1':            iCh = 1;            break;          case '2':            iCh = 2;            break;          case '3':            iCh = 3;            break;          case '4':            iCh = 4;            break;          case '5':            iCh = 5;            break;          case '6':            iCh = 6;            break;          case '7':            iCh = 7;            break;          case '8':            iCh = 8;            break;          case '9':            iCh = 9;            break;          case 'a':            iCh = 10;            break;          case 'b':           iCh = 11;            break;          case 'c':            iCh = 12;            break;          case 'd':            iCh = 13;            break;          case 'e':            iCh = 14;            break;          case 'f':            iCh = 15;            break;          default:            iCh = -1;            break;        }        iPow = power(16, pos);        pos++;        value = iPow * iCh;        result += value;    }    return result;};unsigned long power(int a, int b){    int i;    unsigned long result = 1;    for(i = 0; i < b; i++)        result *= a;            return result;};int toLower(int c){    if(c >= 'A' && c <= 'Z')        return c + 'a' - 'A';    else        return c;};
    
   
  
 

Compiled in CDT.

If you have any questions, please refer to: Using CDT + cygwin to write C/C ++

Note *: Refer to Chapter 6 binary, octal, and hexadecimal system-2nd xuanxiang Nanyu