c语言使用库函数的2、8、10、16进制转换

只用于非负整数

#include<stdio.h>//上个程序是从十进制到任意进制的转换,这个程序是二进制(Binary)八进制(Octonary)十进制(Decimalism)十六进制(Hexadecimal)
#include<stdlib.h>
#include<string.h>
#include<math.h>
#include<ctype.h>
void Binary_To_Decimalism(char base[])
{
    int length = strlen(base);
    //printf("%d\n",length);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(2.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(2.0,length-1-index));
    }

    printf("%lld\n",decimalismtemp);
}
void Binary_To_Octonary(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(2.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(2.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Octonary(Dec);
}
void Binary_To_Hexadecimal(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(2.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(2.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Hexadecimal(Dec);
}
void Decimalism_To_Binary(char base[])
{
    int length = strlen(base),index=0;
    char Bin[40];
    long long DecimalismNumber = atoi(base),divide,remainder;
    //printf("%lld\n",DecimalismNumber);
    /*divide = DecimalismNumber;
    while(divide>0)
    {
        remainder = divide%2;
        Bin[index++] = remainder+'0';
        divide/=2;
    }
    Bin[index]='\0';
    printf("%s\n",Bin);
    strcpy(base,Bin);
    length = strlen(Bin);
    for(index=0;index<length;index++)Bin[index]=base[length-index];*/
    itoa(DecimalismNumber,Bin,2);
    printf("%s\n",Bin);
}
void Decimalism_To_Octonary(char base[])
{
    int length = strlen(base);
    char Oct[40];
    long long DecimalismNumber = atoi(base);
    //printf("%lld\n",DecimalismNumber);
    itoa(DecimalismNumber,Oct,8);
    printf("%s\n",Oct);
 }
void Decimalism_To_Hexadecimal(char base[])
{
    int length = strlen(base);
    char Hex[40];
    long long DecimalismNumber = atoi(base);
    itoa(DecimalismNumber,Hex,16);
    printf("%s\n",Hex);
}
void Octonary_To_Binary(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(8.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(8.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Binary(Dec);
}
void Octonary_To_Decimalism(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(8.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(8.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    printf("%s\n",Dec);
}
void Octonary_To_Hexadecimal(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(8.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(8.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Hexadecimal(Dec);
}
void Hexadecimal_To_Binary(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(16.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(16.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Binary(Dec);
}
void Hexadecimal_To_Octonary(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(16.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(16.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    Decimalism_To_Octonary(Dec);
}
void Hexadecimal_To_Decimalism(char base[])
{
    int length = strlen(base);
    int index;
    long long decimalismtemp = 0;
    for(index=0;index<length;index++)
    {
        decimalismtemp += (base[index]-'0')*(int)pow(16.0,length-1-index);
        //printf("%d\n",(base[index]-'0')*(int)pow(16.0,length-1-index));
    }
    char Dec[40];
    itoa(decimalismtemp,Dec,10);
    printf("%s\n",Dec);
}

int main()
{
    char origin[40];
    int from,to;
    printf("\t这个程序仅支持2、8、10、16进制之间的相互转换\n");
    printf("输入要转换的数: ");
    scanf("%s",&origin);
    printf("这个数的进制?: ");
    scanf("%d",&from);
    printf("要转换为的进制?: ");
    scanf("%d",&to);
    switch(from)
    {
        case 2:
        {
            switch(to)
            {
                case 8:Binary_To_Octonary(origin);break;
                case 10:Binary_To_Decimalism(origin);break;
                case 16:Binary_To_Hexadecimal(origin);break;
            }
            break;
        }
        case 8:
        {
            switch(to)
            {
                case 2:Octonary_To_Binary(origin);break;
                case 10:Octonary_To_Decimalism(origin);break;
                case 16:Octonary_To_Hexadecimal(origin);break;
            }
            break;
        }
        case 10:
        {
            switch(to)
            {
                case 8:Decimalism_To_Octonary(origin);break;
                case 2:Decimalism_To_Binary(origin);break;
                case 16:Decimalism_To_Hexadecimal(origin);break;
            }
            break;
        }
        case 16:
        {
            switch(to)
            {
                case 8:Hexadecimal_To_Octonary(origin);break;
                case 10:Hexadecimal_To_Decimalism(origin);break;
                case 2:Hexadecimal_To_Binary(origin);break;
            }
            break;
        }
    }
    return 0;
}

不使用itoa或atoi的10进制向任意进制转换

#include <stdio.h>
void system_conv(char ss[], int n, int m){
    char s[33];
    int k = 0, t, i, j = 0;
    if ( n == 0 ){  //当数为0，字符串直接是0
        ss[0] = '0';
        ss[1] = '\0';  //给出字符串的结尾
        return;
    }
    if ( n < 0 ){ //负数字符串开头要加负号
        ss[j++] = '-';
        n = -n;//转绝对值才能用
    }
    while ( n > 0 ){
        t = n%m;//取余数并生成序列
        s[k++] = t>9 ? t-10+'A' : t+'0';//根据余数的值赋字符，若余数大于9说明目标进制是10+，采用字母表示一位
        n /= m;//记得要使n变化，退出条件是n到0
    }
    for ( i = k-1; i>=0; --i ){  //将之前生成的字符串逆置
        ss[j++] = s[i];
    }
    ss[j] = '\0'; //给出字符串的结尾，防止由于输出长度产生错误
}
int main(){
    char s[33];
    int n, m;  //n是十进制数，m是转换的目标进制
    while ( ~scanf("%d%d", &n, &m) ){
        system_conv(s, n, m);
        printf("%s\n", s);
    }
    return 0;
}