Exercise 5-2 (getfloat)

Chapter_5     Exercise_5-1

pointers     Exercise_5-3

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Exercise 5-2     K&R, p. 97

Exercise 5-2. Write getfloat(), the floating-point analog of getint(). What type does getfloat() return as its function value?

CONTENTS:     integers.txt     floats.txt     getfloat.c

integers.txt         download

-123 254 120356 145879 +56 +963 -89 78 3254 -852
0123 142587 -8526 45678 231054 52368 +0236 789 2 0

floats.txt         download

-.2 +.3 -1 +02.3 12365 0 -0.2 +0 -9927 -0
-123456789 123456789

getfloat.c         download

#include <stdio.h> // for getchar(), putchar(), printf(), EOF

#define SIZE 100 // array size

int getfloat(float *); // get the next float from input

int main()
{
int i, n;
float array[SIZE];

for (n = 0; n < SIZE; n++)
{
i = getfloat(&array[n]);
if (i == EOF || i == 0) // end of input or not a number
{break;} // out of for()
}
printf("Array size: %d\n", n);
for (i = 0; i < n; i++) // print array
{printf("%g%c", array[i], (i % 10) == 9 ? '\n' : ' ');}
if (n % 10 != 0) {putchar('\n');}

return 0;
}

#include <ctype.h> // for isspace(), isdigit()

int getch(void);
void ungetch(int);

int getfloat(float *pn) // get the next float from input
{
int c, sign;
int digits = 0; // no of digits > 0 for a valid number
float power;

while (isspace(c = getch())) // skip whitespace
{}
if (c == EOF)
{return c;} // return EOF;
if (!isdigit(c) && c != '+' && c != '-' && c != '.')
{
ungetch(c);
return 0; // not a number
}

sign = (c == '-') ? -1 : 1;
if (c == '+' || c == '-')
{c = getch();}
if (!isdigit(c) && c != '.')
{
ungetch(c);
return 0; // not a number
}

for (*pn = 0; isdigit(c); c = getch()) // get integer part
{
digits++;
*pn = 10 * *pn + (c - '0');
}
if (c == '.')
{c = getch();}
for (power = 1.0; isdigit(c); c = getch()) // get fractional part
{
digits++;
*pn = 10 * *pn + (c - '0');
power *= 10.0;
}
*pn *= sign;
*pn /= power;

ungetch(c); // if (c == EOF), it will be returned by the next call to getfloat()

if (digits == 0) // not a valid number, like `+', `-', `.', `-.', `+.'
{return 0;}

return 1; // valid float found
}

// buffer for ungetch():
int buf = EOF-1; // not a real character, not even EOF

int getch(void) // get a (possibly pushed-back) character
{
if (buf < EOF)
{
return getchar();
}

int temp = buf; // buf >= EOF
buf = EOF-1; // reset buf

return temp;
}
// push character back on input (make it available for the next getch()):
void ungetch(int c)
{
buf = c;
}
/*
gcc getfloat.c -o getfloat
./getfloat
a
Array size: 0

./getfloat
a 1
Array size: 0

./getfloat
+.
Array size: 0

./getfloat
1 a
Array size: 1
1

./getfloat
-.2 // Type Enter, then Ctrl^D in Linux or Ctrl^Z + Enter in Windows (EOF)
Array size: 1
-0.2

./getfloat
-.0
Array size: 1
-0

./getfloat
1.2
Array size: 1
1.2

./getfloat
0
Array size: 1
0

./getfloat
-1 +02
Array size: 2
-1 2

./getfloat
0 1 2 3 4 5 6 7 8 9
Array size: 10
0 1 2 3 4 5 6 7 8 9

./getfloat
0 1 2 3 4 5 6 7 8 9 10
Array size: 11
0 1 2 3 4 5 6 7 8 9
10

./getfloat < integers.txt
Array size: 20
-123 254 120356 145879 56 963 -89 78 3254 -852
123 142587 -8526 45678 231054 52368 236 789 2 0

./getfloat < floats.txt
Array size: 12
-0.2 0.3 -1 2.3 12365 0 -0.2 0 -9927 -0
-1.23457e+08 1.23457e+08
*/

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