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utils.h

#ifndef UTILS_H
#define UTILS_H

int Hex2Char(int fromi,char *toc);
int Char2Hex(char fromc,int *toi);
int BitStr2ByteArr(char *bs,char *ba)；
int ByteArr2BitStr(char *ba,char *bs);
int INT2ByteArr(int i,char *ba);
int ByteArr2INT(char *ba,int *i);

#endif

utils.c

#include<stdio.h>
#include<utils.h>
#include<string.h>
int Hex2Char(int fromi,char *toc)
{
    if(fromi>=0&&fromi<=9)
    {
        *toc= fromi+'0';
    } 
    else if(fromi>=10&&fromi<=15)
    {
        *toc = fromi+'A'-10;
    }
    else
    {
        printf("error");
     }
    return 0;
}
int Char2Hex(char fromc,int *toi)
{
    if(fromc>='0'&& fromc<='9')
    {
             *toi= fromc-'0';
    }
    else if(fromc>='A'&& fromc<='F')
    {
             *toi= fromc-'A'+10;
    
        }
        else 
        {
            printf("error");
        }
    return 0;
}

int INT2ByteArr(int i,char *ba){
   int j,a;int sum=0;
   int k=i;
   for(j=0;;j++)
   {
     k=k/16;
     if(k!=0)
      sum++;
     else
       break;
   }
   for(j=sum;j>=0;j--){
     a = i%16;
     Hex2Char(a,&ba[j]);
     i=i/16;   
   }
   ba[sum+1]='\0';
}
int ByteArr2INT(char *ba,int *i)
{
   int len;
   int j;
   int n=0;
   *i=0;
   len = strlen(ba);
   for(j=0;j<len;j++)
   {
      Char2Hex(ba[j],&n);
      *i=(*i)*16+n;  
   }
   
}

main.c

#include<stdio.h>
#include"utils.h"
int main(){
  int p;
  char bytearr[100];
  printf("请输入一个整型数字\n");
  scanf("%d",&p);
  printf("把整型数转化为字节数组\n");
  INT2ByteArr(p,bytearr);
  printf("字节数组为%s\n",bytearr);
 
  char barr[100];
  int h;
  printf("请输入一个字节数组:");
  scanf("%s",barr);
  printf("把字节数组转化为整型数字:");
  ByteArr2INT(barr,&h);
  printf("%d\n",h);
   

}

运行结果