Effect of adding whitespace in the scanf() function in C

In this article, we will discuss the scenarios regarding adding white space before or after the format specifier in a scanf() function in C Programming Language.

Adding a whitespace character in a scanf() function causes it to read elements and ignore all the whitespaces as much as it can and search for a non-whitespace character to proceed.

scanf("%d ");
scanf(" %d");

scanf("%d\n"); This is different
from scanf("%d"); function.

Example 1: The scanf function after reading the number starts reading further until it finds a non-whitespace character on the input and prints the first number that was typed.

Adding whitespace or “\n” after format specifier in scanf function
scanf(“%d “); 
         or 
scanf(“%d\n”, );

Below is the C program to implement the above approach:

C

// C program to demonstrate the
// above approach

#include <stdio.h>

// Driver Code
int main()
{
    // Declaring integer variable a
    int a;

    // Reading value in "a" using scanf
    // and adding whitespace after
    // format specifier
    scanf("%d ", &a);

    // Or scanf("%d\n", &a);

    // Both work the same and
    // print the same value
    printf("%d", a);

    return 0;
}

Output:

Explanation: In the above example, when the program is executed, first the program will ask for the first input.

• In this case, 2 is entered, after that whitespace is given and still there is no output rather waiting for the next input.
• When 3 is entered, the output is printed which is the first number that is entered i.e., 2.
• Similarly, is the case when after entering the first input i.e., 2 in the above case, if the user presses enter button and goes to the next line, the program is still waiting for the input and after entering the second input the result is printed.

Example 2: The scanf function ignores the whitespace character and reads the element only once.

Adding whitespace before format specifier in scanf function
scanf(” %d”);

Below is the C program to implement the above approach:

C

// C program to demonstrate the
// above approach
#include <stdio.h>

// Driver Code
int main()
{
    // Declaring integer variable
    int a;

    // Reading value in a using scanf
    // and adding whitespace before
    // format specifier
    scanf(" %d", &a);

    // Printing value of a
    printf("%d", a);

    return 0;
}

Output:

Explanation: In this code, there is an output as soon as the number is entered because almost all the whitespaces before format specifier are ignored by scanf %-conversions except for “%c”, “%n”, and “%[“. Hence, it is advised to avoid whitespaces in scanf function as much as possible unless one is confident of its use and necessity.