Step by Step solution about How to resolve the algorithm Determine if a string is numeric step by step in the C programming language

This C code defines a function called isNumeric that takes a constant character pointer (const char *) as its input and returns an integer indicating whether the input string represents a numeric value. Here's a detailed breakdown of the code:

1. Function Signature:

   int isNumeric (const char * s)

   This line declares the isNumeric function, which takes a single argument:

   • s: A constant character pointer that points to the input string to be checked for numeric value.

2. Input Validation:

   if (s == NULL || *s == '\0' || isspace(*s))

   This if statement checks for invalid input conditions:

   • s == NULL: If the input pointer is NULL, it means there's no string to check.
   • *s == '\0': If the first character of the string is the null character ('\0'), it means the string is empty.
   • isspace(*s): If the first character is a whitespace character (e.g., space, tab, newline), the input is not considered numeric. If any of these conditions are met, the function returns 0, indicating that the input is not numeric.

3. String-to-Double Conversion:

   char * p;
   strtod (s, &p);

   These lines perform string-to-double conversion using the strtod function:

   • strtod: This function converts a string (s) to a double-precision floating-point number (double) and stores the result in the variable pointed to by p.
   • p: This is a pointer to a character that will point to the first character in the string that was not converted to a number.

4. Numeric Check:

   return *p == '\0';

   After the string-to-double conversion, the function checks if the entire input string was successfully converted to a number:

   • *p == '\0': If this condition is true, it means that the entire input string was converted to a number and there were no non-numeric characters remaining in the string. In this case, the function returns 1, indicating that the input is numeric.

If the entire input string was not successfully converted to a number (i.e., *p points to a non-numeric character), the function returns 0, indicating that the input is not numeric.

#include <ctype.h>
#include <stdlib.h>
int isNumeric (const char * s)
{
    if (s == NULL || *s == '\0' || isspace(*s))
      return 0;
    char * p;
    strtod (s, &p);
    return *p == '\0';
}