数字按照不同格式转换成字符串

　　如果自己写函数，不使用itoa怎么判断呢？

　　我们用通常的办法，对数字进行每位的除商，得到后与字符'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，我们设置标志位flag,为1之前的所有0都不输出。当flag为1时，进行转换。

　　全部代码可以参考：

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 //蔡健雅 双栖动物
  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 }