K & R C Programs Exercise 4-2.

K and R C, Solution to Exercise 4-2:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
Write a C Program to extend the atof function to handle scientific notations of the form 5234.73e-12
atof function converts the intial nptr string to the double. atof means ASCII to float. In this program that atof function handles the scientific notations also like 12.e-3.. Read more about C Programming Language .

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#include <ctype.h>
#include <limits.h>
#include <float.h>
#include <signal.h>
#include <stdio.h>

int my_atof(char *string, double *pnumber) {
/* Convert char string to double data type. */
double retval;
double one_tenth = 0.1;
double ten = 10.0;
double zero = 0.0;
int found_digits = 0;
int is_negative = 0;
char *num;

/* Check pointers. */
if (pnumber == 0) {
return 0;
}
if (string == 0) {
*pnumber = zero;
return 0;
}
retval = zero;

num = string;

/* Advance past white space. */
while (isspace(*num))
num++;

/* Check for sign. */
if (*num == '+')
num++;
else if (*num == '-') {
is_negative = 1;
num++;
}
/* Calculate the integer part. */
while (isdigit(*num)) {
found_digits = 1;
retval *= ten;
retval += *num - '0';
num++;
}

/* Calculate the fractional part. */
if (*num == '.') {
double scale = one_tenth;
num++;
while (isdigit(*num)) {
found_digits = 1;
retval += scale * (*num - '0');
num++;
scale *= one_tenth;
}
}
/* If this is not a number, return error condition. */
if (!found_digits) {
*pnumber = zero;
return 0;
}
/* If all digits of integer & fractional part are 0, return 0.0 */
if (retval == zero) {
*pnumber = zero;
return 1; /* Not an error condition, and no need to
* continue. */
}
/* Process the exponent (if any) */
if ((*num == 'e') || (*num == 'E')) {
int neg_exponent = 0;
int get_out = 0;
long index;
long exponent = 0;
double getting_too_big = DBL_MAX * one_tenth;
double getting_too_small = DBL_MIN * ten;

num++;
if (*num == '+')
num++;
else if (*num == '-') {
num++;
neg_exponent = 1;
}
/* What if the exponent is empty? Return the current result. */
if (!isdigit(*num)) {
if (is_negative)
retval = -retval;

*pnumber = retval;

return (1);
}
/* Convert char exponent to number <= 2 billion. */
while (isdigit(*num) && (exponent < LONG_MAX / 10)) {
exponent *= 10;
exponent += *num - '0';
num++;
}

/* Compensate for the exponent. */
if (neg_exponent) {
for (index = 1; index <= exponent && !get_out; index++)
if (retval < getting_too_small) {
get_out = 1;
retval = DBL_MIN;
} else
retval *= one_tenth;
} else
for (index = 1; index <= exponent && !get_out; index++) {
if (retval > getting_too_big) {
get_out = 1;
retval = DBL_MAX;
} else
retval *= ten;
}
}
if (is_negative)
retval = -retval;

*pnumber = retval;

return (1);
}

double atof(char *s) {
double d = 0.0;
if (!my_atof(s, &d)) {
#ifdef DEBUG
fputs("Error converting string in [sic] atof()", stderr);
#endif
raise(SIGFPE);
}
return d;
}

#ifdef UNIT_TEST
char *strings[] = {
"1.0e43",
"999.999",
"123.456e-9",
"-1.2e-3",
"1.2e-3",
"-1.2E3",
"-1.2e03",
"cat",
"",
0
};
int main(void)
{
int i = 0;
for (; *strings[i]; i++)
printf("atof(%s) = %gn", strings[i], atof(strings[i]));
return 0;
}
#endif

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C Program to demonstrate the ‘atof’ and ‘gets’ functions.

C Program to demonstrate the ‘atof’ and ‘gets’ functions. atof function converts the intial nptr string to the double. atof means ASCII to float. gets function reads string from the input stream. puts function prints string to the output stream This program will multiply to floating point numbers. The program will accept invalid data, and give you crap results as a result. Read more about C Programming Language .

/***********************************************************
* You can use all the programs on www.c-program-example.com
* for personal and learning purposes. For permissions to use the
* programs for commercial purposes,
* contact [email protected]
* To find more C programs, do visit www.c-program-example.com
* and browse!
*
* Happy Coding
***********************************************************/



#include <stdio.h>
#include <stdlib.h>

main()
{
char str1[80], str2[80]; /* define a couple o' strings. */
double result; /* Result of multiplication. */

puts ("This program will multiply to floating point numbers.");
puts ("The program will accept invalid data, and give you");
puts ("crap results as a result.n");
puts ("Please enter the first number.");
gets(str1);

puts ("And the second.");
gets(str2);

result = atof(str1) * atof(str2);
printf("Answer is %8.2fn", result);
}


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