# Exercise 5.2 - get next float from input to *pn¶

## Question¶

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

```/*Write a program to get next float from input to *pn */

#include<stdio.h>
#include<ctype.h>

#define SIZE 1000

int getch(void);

void ungetch(int);

int getfloat(float *);

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

for (n = 0; n < SIZE && getfloat(&array[n]) != EOF; n++);
for (; n >= 0; n--)
printf("%f", array[n]);

return 0;
}

int getfloat(float *pn) {
int c, sign;
float power;

while (isspace(c = getch()));

if (!isdigit(c) && c != EOF && c != '+' && c != '-' && c != '.') {
ungetch(c);
return 0;
}

sign = (c == '-') ? -1 : 1;

if (c == '+' || c == '-')
c = getch();

for (*pn = 0.0; isdigit(c); c = getch())
*pn = 10.0 * *pn + (c - '0');
if (c == '.')
c = getch();

for (power = 1.0; isdigit(c); c = getch()) {
*pn = 10.0 * *pn + (c - '0');    /* fractional part */
power *= 10.0;
}

*pn *= sign / power;

if (c != EOF)
ungetch(c);

return c;
}

#define BUFSIZE 100

char buf[BUFSIZE];
int bufp = 0;

int getch(void) {
return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c) {
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}

```

## Explanation¶

The function getfloat is similar to the getint function, wherein instead of getting an integer, we get a float value.

We declare an array, float array[SIZE] in which we store the float values and the the float value is got from the function int getfloat(float *);

The function getfloat, sends a pointer to the float and stores a float value in the array. The mechanism of how it gets a float is defined in the getfloat function.

The curx of how the float is got is in this snippet. The function reads all the characters and converts to a float and stores them in the *pn pointer. Then it reads the decimal part and for all the digits after the decimal point, it increments the power by 10. For e.g. if the decimal was 0.123 for 3 decimal digits, the power will be 10 * 10 * 10 = 1000.

```for(*pn = 0.0 ; isdigit(c);c=getch())
*pn = 10.0 * *pn + (c - '0');
if( c == '.')
c = getch();

for(power=1.0;isdigit(c);c=getch())
{
*pn = 10.0 * *pn + (c - '0');   /* fractional part */
power *= 10.0;
}

*pn  *= sign / power;
```

Finally to get the decimal representation along with sign, then the number in pn is divided by power and multiplied by sign, i.e, *pn = ((*pn * sign) / power) and thus the correct float value is obtained.

The float value is stored in the array index that was sent from the main program.