數字按照不一樣格式轉換成字符串

　　若是本身寫函數，不使用itoa怎麼判斷呢？

　　咱們用一般的辦法，對數字進行每位的除商，獲得後與字符'0'相加。

flag = 0; for(i=0;i<6;i++){ tmp = int(num/pow(10,5-i)); if(tmp != 0){ *str = 1; flag = 1; } if(*str != 0 || flag){ *str++ = tmp+'0'; num = num%int(pow(10,5-i)); } } 

 

　　要注意的就是，咱們設置標誌位flag,爲1以前的全部0都不輸出。當flag爲1時，進行轉換。

　　所有代碼能夠參考：

 1 #include <stdio.h>
 2 #include <stdlib.h>
 3 //蔡健雅 雙棲動物
 4 int myitoa(int num,char *str,int n);  5 int pow(int num,int n);  6 int main(){  7     int num = 100;  8     char str[15];  9     myitoa(100,str,16);  10     printf("number %d binary %s\n",num,str);  11     myitoa(100,str,10);  12     printf("number %d binary %s\n",num,str);  13     myitoa(100,str,8);  14     printf("number %d binary %s\n",num,str);  15     myitoa(100,str,2);  16     printf("number %d binary %s\n",num,str);  17  getchar();  18     return 0;  19 }  20 int pow(int num,int n){  21     int i;  22     int result = 1;  23     for(i=0;i<n;i++){  24         result *= num;  25  }  26     return result;  27 }  28 int myitoa(int num,char *str,int n){  29     if(str == NULL)  30         return -1;  31     if(num < 0){  32         *str++ = '-';  33         num = 0 - num;  34  }  35     int i;  36     int tmp = 0;  37     int flag = 0;  38     *str = 0;  39     switch(n){  40     case 16:  41         flag = 0;  42         for(i=0;i<8;i++){  43             tmp = int(num/pow(16,7-i));  44             if(tmp != 0){  45                 *str = 1;  46                 flag = 1;  47  }  48             if(*str != 0 || flag){  49                 if(tmp >= 0 && tmp <= 9){  50                     *str++ = tmp+'0';  51                 }else if(tmp >= 10 && tmp <= 15){  52                     *str++ = tmp-10+'A';  53  }  54                 num = num%int(pow(16,7-i));  55  }  56  }  57         break;  58     case 10:  59         flag = 0;  60         for(i=0;i<6;i++){  61             
 62             tmp = int(num/pow(10,5-i));  63             if(tmp != 0){  64                 *str = 1;  65                 flag = 1;  66  }  67             if(*str != 0 || flag){  68                 *str++ = tmp+'0';  69                 num = num%int(pow(10,5-i));  70  }  71  }  72         break;  73     case 2:  74         flag = 0;  75         for(i=0;i<32;i++){  76             tmp = int(num/pow(2,31-i));  77             if(tmp != 0){  78                 *str = 1;  79                 flag = 1;  80  }  81             if(*str != 0 || flag){  82                 *str++ = tmp+'0';  83                 num = num%int(pow(2,31-i));  84  }  85  }  86         break;  87     case 8:  88         flag = 0;  89         for(i=0;i<10;i++){  90             tmp = int(num/pow(8,9-i));  91             if(tmp != 0){  92                 *str = 1;  93                 flag = 1;  94  }  95             if(*str != 0 || flag){  96                 *str++ = tmp+'0';  97                 num = num%int(pow(8,9-i));  98  }  99  } 100         break; 101  } 102     *str = '\0'; 103     return 0; 104 }

 

　　運行結果爲：