Converting string, to float (without atof) in C

Question

I'm designing a function that will convert a string into a float.
e.g. "45.5" = 45.5

I have this so far. But it doesn't seem to work. Keep in mind, we cannot use any C library functions like atoi, atof or even pow for that matter.

int str2float( char *s )

{

    int num = 0;

    int dec = 0;

    double i = 1.0;

    int ten = 1;

    /***** ADD YOUR CODE HERE *****/



    for(; *s != '\0'; s++)

    {

        if (*s == '.'){

            for(; *s != '\0'; s++){

                dec = (dec * CONT) + (*s - '0');

                i++;

            }

        }else{

            num = (num * CONT) + (*s - '0');

        }



    }

    for(;i!=0;i--){

        ten *= 10;

    }

    dec = dec / (ten);

    printf("%d", dec);

    num += dec;

    return num;  

}

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Answer 1

Here is my try:

float stof(const char* s){
  float rez = 0, fact = 1;
  if (*s == '-'){
    s++;
    fact = -1;
  };
  for (int point_seen = 0; *s; s++){
    if (*s == '.'){
      point_seen = 1; 
      continue;
    };
    int d = *s - '0';
    if (d >= 0 && d <= 9){
      if (point_seen) fact /= 10.0f;
      rez = rez * 10.0f + (float)d;
    };
  };
  return rez * fact;
};

Converting string, to float (without atof) in C

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