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0ss[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;
}