Converts a numeric string to the corresponding digital output (regardless of overflow)

Use C to write a function that converts a numeric string to a corresponding number, regardless of overflow, (e.g. "12.34" to a number: 12.34), considering an exception input

Thinking: Exceptions such as entering subtitles, etc., may also be entered ' + ', '-' and so on,

The procedure is as follows:

#include <stdio.h> #include <stdlib.h> #include <assert.h>double my_atof (const char* &NBSP;STR) {assert (str);d ouble num = 0;int flag = 0;int point = 0; while  (*STR) {int value = 1;if  ('-'  == *str && 0 ==  flag) flag = -1;else if  ('-'  == *str && 1 ==  Flag) flag = -1;else if  ('-'  == *str && -1 == flag) flag = 1;else if  (' + '  == *str && 0 == flag) flag  = 1;if  (*str ==  '. ') &&point == 0) point++;int temp = point;if  ((*str >=  ' 0 ')  &&  (*str <=  ' 9 ')  &&  (0 == point)) num =  10 * num + *str -  ' 0 ';else if  (*str >=  '0 ')  &&  (*str <=  ' 9 ')  &&  (point > 0)) {temp--; while  (temp--) value = value * 10;num = num +  (double) (*str -   ' 0 ')  / value;} str++;if  (point > 0) point++;} if  ( -1 == flag) Num = -num;return num;} Int main () {double n, m;char buffer[256];p rintf ("enter degrees: "); fgets (buffer,  256, stdin); n = my_atof (buffer);p rintf ("the number is: %f \n",  n ); System ("pause"); return 0;}

Please correct me if there is any mistake or consideration.

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Converts a numeric string to the corresponding digital output (regardless of overflow)