浮点数的输入(C语言控制台程序)

//2010-3-28 #include <stdio.h> int IsValid (int ch);//输入字符是否合法 void StrToFloat (double* dou, char* str);//转化为浮点数 void StrInput (char* out);//浮点字符串的输入 int main (void) { char out[32];//输出的字符串 StrInput (out);//浮点数输入 printf ("您的输入为: %s\n", out); return 0; } void StrInput (char* out)//浮点字符串的输入 { int index = -1;//数组索引 int ch;//接受字符 double dou; int flag = 0; printf ("输入浮点数:\t"); while (1) { if (index > 31)//最大长度字符串 { printf ("字符串长度大于32，重输:\t"); fflush (stdin); index = -1; flag = 0; continue; } ch = getchar (); if (IsValid (ch)) { if ('.' == ch)//输入为. { if (1 == flag)//已经输入了. { printf ("输入不合法，重输:\t"); fflush (stdin); index = -1; flag = 0; continue; } flag = 1; out[++ index] = ch; continue; }//end if ('.' == ch) else if (ch >= '0' && ch <= '9' || '-' == ch)//输入为数字或'-' out[++ index] = ch; else if (' ' == ch || '\t' == ch)//空格或tab continue; else//回车退出 { out[++ index] = '\0'; break; } }//end if (IsValid (ch)) else//输入不合法 { fflush (stdin); index = -1; flag = 0; } }//end while (1) StrToFloat (&dou, out); printf ("浮点数为%lf\n", dou); } int IsValid (int ch)//输入字符是否合法 { if (ch >= '0' && ch <= '9' || '.' == ch || '\n' == ch || ' ' == ch || '\t' == ch || '-' == ch) return 1;//1...9、.、'\n'、空格、\t、'-'合法 else return 0; } void StrToFloat (double* dou, char* str)//转化为浮点数 { int flag = 0;//小数点到来的标志 int index = -1;//数组索引 double down = 1;//分母 double up = 0;//分子 for (index = 0; '\0' != str[index]; ++ index) { if ('-' == str[index])//负数 continue; else if ('.' == str[index]) { flag = 1; continue; } else up = 10 * up + (str[index] - '0'); if (1 == flag) down *= 10; } *dou = up * 1.0 / down; if ('-' == str[0])//负数 *dou *= -1; }