Input-Output Techniques and key concepts of using printf-scanf

Input-Output Techniques:
 
In all programming competition, or more specially, in all useful program, you require to read in input and process it. Though, the input data can be as horrible as possible, and this can be very troublesome to the parse.

If you spend too much time in the coding how to parse the input proficiently and you are utilizing C/C++ as your programming language, then this tip is especially for you. Let us see an illustration:

How to read the following input:
1 2 2 3 1 2 3 1 2 
The fastest method to do it is:

#include <stdio.h>
int N;
void main() {
while(scanf("%d",&N==1)){
    process N…  }
}

There are N lines; each line always begins with character '0' followed by '.', then unknown number of digits x, lastly the line always terminated by three dots "...".

N
0.xxxx...

The fastest method to do it is:

#include <stdio.h>
char digits[100];
void main() {
scanf("%d",&N);
for (i=0; i<N; i++) {
    scanf("0.%[0-9]...",&digits); // surprised?
    printf("the digits are 0.%s\n",digits);
  }
}

This is the trick which many C/C++ programmers do not aware of. Why we state C++ while scanf/printf is a standard C I/O routine? This is since most of the C++ programmers "forcing" themselves to employ cin/cout all the time, devoid of realizing that scanf/printf can still be employed within all C++ programs. 

Advanced use of printf() and scanf():

Such who have forgotten the advanced use of printf() and scanf(), remind the following illustrations:

scanf("%[ABCDEFGHIJKLMNOPQRSTUVWXYZ]",&line);
//line is a string

This scanf() function takes just upper-case letters as input to line and any other characters other than A….Z terminates the string. Likewise the following scanf() will behave like gets():

scanf("%[^\n]",line); //line is a string

Learn the default terminating characters for the scanf().

Using new line with scanf():

When the content of a file (input.txt) is

abc
def

And the following program is performed to take input from file:

char input[100],ch;
void main(void)
{
    freopen("input.txt","rb",stdin);
    scanf("%s",&input);
    scanf("%c",&ch);
}
The following is a small modification to code: 
char input[100],ch;
void main(void)
{
    freopen("input.txt","rb",stdin);
    scanf("%s\n",&input);
    scanf("%c",&ch);
}

What will be their respective value? The value of ch will be '\n' for the first code and 'd' for second code.

Be careful about using gets() and scanf() together:

You must as well be careful about using gets() and scanf() in similar program. Test it with the following scenario. Code is as shown below:

scanf("%s\n",&dummy);
gets(name);
And the input file is:
ABCDEF 
bbbbbXXX

What do you obtain as the value of name? "XXX" or "bbbbbXXX" (Here, ‘b’ signifies blank or space)

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