80. Convert a String to Float

You are given a null-terminated string representing a floating-point number, which may contain:

• An optional sign (+ or -)
• A decimal point
• Only valid digits and one dot

Your task is to convert this string to its floating-point value (float), without using standard library functions like atof() or strtof().

Do not handle scientific notation (e.g., "1.2e5").

Example-1

Input: "123.45"
Output: 123.45

Example-2

Input: "-0.75"
Output: -0.75

Example-3

Input: "100"
Output: 100.00

Example-4

Input: "+9.99"
Output: 9.99