Exercise 3-6 (itoap - Integer to string, padded)

Chapter_3     Exercise_3-5

trim     Chapter_4

---

---

Exercise 3-6     K&R, p. 64

Exercise 3-6. Write a version of itoa() that accepts three arguments instead of two. The third argument is a minimum field width; the converted number must be padded with blanks on the left if necessary to make it wide enough.

itoap.c         download

#include <stdio.h> // for printf(), scanf()

#define SIZE 100 // array size (max no of digits)
#define WIDTH 8 // could also be 16, 32, or 64

// reverse s[], knowing its length:
void reverse(char s[], int len);
// int to string of chars, minimum field width:
int itoap (int n, char s[], unsigned width);

int main()
{
char digits[SIZE];
int n;

printf ("Give an integer: ");
scanf ("%d", &n);

itoap(n, digits, WIDTH);

printf ("%s\n", digits); // with an eventual sign

return 0;
}
// reverse s[], knowing its length:
void reverse(char s[], int len)
{
int i = 0, j = len-1;
char temp;

while (i < j)
{
temp = s[i];
s[i] = s[j];
s[j] = temp;
i++;
j--;
}
}
// get the digits of n into s[] (convert n to a string of characters),
// with a minimum field width (padded to the left if necessary),
// return length of s[] (digits, eventual sign):
int itoap (int n, char s[], unsigned width)
{
int i = 0, sign = 1, diff;

if (n < 0)
{
sign = -1;
}

do
{ // get the digits in reverse order:
s[i++] = (n % 10)*sign + '0'; // get next (last read) digit
// if n < 0, (n /= 10) <= 0, (n % 10) < 0
} while (n /= 10); // while ((n /= 10) != 0); // delete last digit

if (sign < 0) {s[i++] = '-';} // first char after reverse

diff = width-i;
while (diff > 0) // while (diff)
{
s[i++] = ' ';
diff--;
}

s[i] = '\0'; // end the string

reverse(s, i);

return i;
}
/*
gcc itoap.c -o itoap
./itoap
Give an integer: 0
0

./itoap
Give an integer: -1
-1

./itoap
Give an integer: 123
123

./itoap
Give an integer: -125
-125

./itoap
Give an integer: 1234567
1234567

./itoap
Give an integer: 12345678
12345678

./itoap
Give an integer: 123456789
123456789

./itoap
Give an integer: -123456
-123456

./itoap
Give an integer: -1234567
-1234567

./itoap
Give an integer: -12345678
-12345678
*/

---

---

Chapter_3     Exercise_3-5

BACK_TO_TOP

trim     Chapter_4