atof函數擴充

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k&r習題4-2，擴充使可以處理科學計數法形式

#include<ctype.h>double atof(char s[]){double val, power, e_sum;int e_val;int i, sign, e_sign;for (i = 0; s[i] == ‘ ‘; i++);sign = (s[i] == ‘-‘) ? (-1) : 1;if (s[i] == ‘+‘ || s[i] == ‘-‘)i++;for (val = 0.0; isdigit(s[i]); i++)val = 10.0 * val + (s[i] - ‘0‘);if (s[i] == ‘.‘)i++;for (power = 1.0; isdigit(s[i]); i++) {val = 10.0 * val + (s[i] - ‘0‘);power *= 10.0;}if (s[i] == ‘e‘ || s[i] == ‘E‘)i++;e_sign = (s[i] == ‘-‘) ? (-1) : 1;e_sum = 1.0;if (s[i] == ‘+‘ || s[i] == ‘-‘)i++;for (e_val = 0; isdigit(s[i]); i++)e_val = 10 * e_val + (s[i] - ‘0‘);for (i = 0; i < e_val; i++) {if (e_sign > 0)e_sum *= 10;elsee_sum /= 10;}return sign * val / power * e_sum;}

這是自己寫的那個，思路比較簡單，基本就是前面步驟的複製，只不過判斷的內容換了，這樣就顯得又臭又長。
答案上那個簡潔些，沒增加新的變數，用了前面的。

atof函數擴充