Basics of the Scanf Function

Introduction to the Scanf Function

The scanf() function is designed to receive multiple user inputs. While it may resemble the printf() function we’ve previously discussed, its functionality differs significantly.

Here is the general syntax of the scanf() function:

scanf(format string, &var1, &var2, ...)

Similar to printf(), scanf() requires a format string that consists of ordinary characters and format specifiers. Additionally, there is no explicit limit to the number of variables that can be passed to this function. As a result, it is theoretically possible to accept an unlimited number of inputs.

Working of Scanf

Consider the following C program:

#include <stdio.h>

int main()
{
    int x;
    scanf("%d", &x);
    printf("The value of x is %d", x);
    return 0;
}

In this C program, the scanf() function is used to receive an integer input from the user. You are encouraged to save the program with any desired name (e.g., scanf-in-action.c) and execute it.

The program begins with the inclusion of the stdio.h header file, which is required to access the printf and scanf functions. Within the main function, an integer variable named x is declared.

By using the scanf() function, the program waits for the user to input an integer. The format specifier %d is employed within the format string of scanf to specify that an integer input is expected. The address of variable x, denoted by &x, is passed as the second argument to scanf(). This ensures that the input value is stored in the memory location associated with variable x.

After the user provides an input, the printf() function is employed to display the value of x. The format specifier %d is used within the format string of printf to indicate that the value to be displayed is an integer.

It is worth noting the distinction between printf() and scanf(). While they have a similar structure, there is a small difference. Every variable in the scanf function is preceded by an &. Why is that so? What does it mean? 

Meaning of Ampersand (&)

In C, the ampersand symbol (&) is known as the “address-of” operator. Its purpose is to provide access to the memory address of an object. In programming, a variable is simply a name associated with a specific block of memory inside the computer.

For instance, let’s consider the variable declaration:

int x = 5;

What does this statement mean? It means that the name “x” is used to refer to a particular block of memory, and the value 5 is stored in that memory block. Whenever we want to access this stored value, we can simply use the variable name “x”. This is why we always write the variable name in the printf() function, as we want to display the content of the variable.

However, when dealing with the scanf() function, things work differently. The scanf() function does not require the content of the variable. In fact, in our example program, the variable does not contain any specific content. Instead, scanf() needs to place the value entered by the user into the variable “x”. To achieve this, scanf() requires the memory address of the variable “x” so that it can store the user input in that specific memory location.

C provides us with the “address-of” operator (&) to access the memory address of a variable. By using the “&” operator, we can obtain the address of a variable, which in turn represents the address of the associated memory block.

To summarize, the “address-of” operator (&) in C allows us to access the memory address of a variable, which corresponds to the memory associated with the variable’s name. Let’s consider the same program once again.

#include <stdio.h>

int main()
{
    int x;
    scanf("%d", &x);
    printf("The value of x is %d", x);
    return 0;
}

Imagine the user enters the value 10. Inside the scanf function, the “&x” part gives the specific location in the computer’s memory where the variable x is stored. This helps scanf() to know where to store the user’s input, which in this case is the value 10.

In contrast, the printf() function works differently. It takes the value stored in the memory location associated with the variable x, which is 10 in our example. Then, it replaces the format specifier %d with this value, so when the program is executed, it will display the number 10.

To summarize, scanf() uses the address of the memory block where the variable x is stored to store the user’s input, while printf() retrieves the value stored in that memory block and displays it using the format specifier %d.

Output:

10
The value of x is 10
Process returned 0 (0x0)    execution time : 3.134 s
Press any key to continue.

When you run the program, you will see a blinking cursor indicating that it is waiting for you to enter something. This is where you can provide the input value. After entering the correct value, you need to press the enter key on your keyboard. This tells the scanf() function that you have finished entering the input.

As soon as you press enter, the program will move to the next line, and you will see the text displayed by the printf() function. In this particular case, the text will be “The value of x is 10”. This line shows the output of the program, where the value you entered is substituted in place of the %d format specifier.

In summary, after providing the input value and pressing enter, you will see the result of the program displayed on the next line, showing the value of x. This demonstrates how the scanf() function works together with the printf() function.