atoi函数的使用实例：【Ubuntu环境】

main.c:

1 #include 
      
        2 #include 
       
         3 extern int factorial(int f);    //external function：如果写extern是显式的外部声明;不写也对，只是隐式的而已 4  5 int main(int argc, char ** argv) 6 { 7         int t; 8         if(argc < 2) 9         {10                 printf("The format of the input: %s number\n", argv[0]);11                 return -1;12         }13         else14         {15                 t = atoi(argv[1]);16                 printf("%d! is %d.\n", t, factorial(t));17         }18         return 0;19 }
       
      

 

factorial.c:

1 #include 
      
       2 3 int factorial(int f)4 {5         if(f <= 1)6                 return 1;7         else8                 return factorial(f - 1) * f;9 }
      

 

编译运行：

Compile:

lxw@lxw-Aspire-4736Z:~/lxw0109/C++$ gcc -o factorial main.c factorial.c

Execute:

lxw@lxw-Aspire-4736Z:~/lxw0109/C++$ ./factorial 4

4! is 24.

lxw@lxw-Aspire-4736Z:~/lxw0109/C++$ ./factorial 5

5! is 120.

 

附：atoi函数的一种实现：

1 int myAtoi(const char* str)  2 {  3     int sign = 0,num = 0;  4     assert(NULL != str);  5     while (*str == ' ')  6     {  7         str++;  8     }  9     if ('-' == *str) 10     { 11         sign = 1; 12         str++; 13     } 14     while ((*str >= '0') && (*str <= '9')) 15     { 16         num = num * 10 + (*str - '0'); //就是这一行，将对应字符转化为数字17         str++; 18     } 19     if(sign == 1) 20         return -num; 21     else 22         return num; 23 }