#includedouble 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; else e_sum /= 10; } return sign * val / power * e_sum;}
这是自己写的那个，思路比较简单，基本就是前面步骤的复制，只不过判断的内容换了，这样就显得又臭又长。 答案上那个简洁些，没增加新的变量，用了前面的。