CODEWITHSUNDEEP
c
Technovicez
Technovicez

Reputation: 13

Input taking spaces by default in c

In the below program when am reading input from keyboard its taking only 2 characters instead of 4 and remaining 2 characters its taking spaces by default. why is it???

program to take char input through pointers/

int c,inc,arrysize;
char *revstring;
printf("enter the size of char arry:");
scanf("%d",&arrysize);
revstring = (char *)malloc(arrysize * sizeof(*revstring));
printf("%d",sizeof(revstring));
printf("enter the array elements:");
for(inc=0;inc<arrysize;inc++)
{
scanf("%c",&revstring[inc]);

}
for(inc =0;inc<arrysize;inc++)
    printf("%c",revstring[inc]);
getch();
return 0;

}

Upvotes: 1

Views: 116

Answers (2)

Chris Dodd
Chris Dodd

Reputation: 126358

Most of the time scanf reads formatted input. For most % formats, scanf will first read and discard any whitespace and then parse the item specified. So with scanf("%d", ... it will accept inputs with initial spaces (or even extra newlines!) with no problems.

One of the exceptions, however, is %c. With %c, scanf reads the very next character, whatever it may be. If that next character is a space or newline, that is what you get.

Depending on what exactly you want, you may be able to just use a blank space in your format string:

scanf(" %c",&revstring[inc]);

The space causes scanf to skip any whitespace in the input, giving you the next non-whitespace character read. However, this will make it impossible to enter a string with spaces in it (the spaces will be ignored). Alternately, you could do scanf(" "); before the loop to skip whitespace once, or scanf("%*[^\n]"); scanf("%*c"); to skip everything up to the next newline, and then skip the newline.

Upvotes: 0

md5
md5

Reputation: 23707

scanf reads formatted inputs. When you tape a number, you tape the digits, and then, you press <Enter>. So there is a remaining \n in stdin, which is read in the next scanf. The same applies if you press <Enter> between the characters.

A solution is to consume the characters in the standard input stream after each input, as follow:

#include <stdio.h>

void
clean_stdin (void)
{
  int c;

  while ((c = getchar ()) != '\n' && c != EOF)
    ;
}

Another idea is to use fgets to get human inputs. scanf is not suitable for such readings.

Upvotes: 3

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