C Input Output (I/O)

C Output

In C programming, printf() is one of the main output function. The function sends formatted output to the screen. For example,

Example 1: C Output

Output

C Programming

How does this program work?

• All valid C programs must contain the main() function. The code execution begins from the start of the main() function.
• The printf() is a library function to send formatted output to the screen. The function prints the string inside quotations.
• To use printf() in our program, we need to include stdio.h header file using the #include <stdio.h> statement.
• The return 0; statement inside the main() function is the "Exit status" of the program. It's optional.

Example 2: Integer Output

Output

Number = 5

We use %d format specifier to print int types. Here, the %d inside the quotations will be replaced by the value of testInteger.

Example 3: float and double Output

Output

number1 = 13.500000
number2 = 12.400000

To print float, we use %f format specifier. Similarly, we use %lf to print double values.

Example 4: Print Characters

Output

character = a

To print char, we use %c format specifier.

C Input

In C programming, scanf() is one of the commonly used function to take input from the user. The scanf() function reads formatted input from the standard input such as keyboards.

Example 5: Integer Input/Output

Output

Enter an integer: 4
Number = 4

Here, we have used %d format specifier inside the scanf() function to take int input from the user. When the user enters an integer, it is stored in the testInteger variable.

Notice, that we have used &testInteger inside scanf(). It is because &testInteger gets the address of testInteger, and the value entered by the user is stored in that address.

Example 6: Float and Double Input/Output

Output

Enter a number: 12.523
Enter another number: 10.2
num1 = 12.523000
num2 = 10.200000

We use %f and %lf format specifier for float and double respectively.

Example 7: C Character I/O

Output

Enter a character: g
You entered g

When a character is entered by the user in the above program, the character itself is not stored. Instead, an integer value (ASCII value) is stored.

And when we display that value using %c text format, the entered character is displayed. If we use %d to display the character, it's ASCII value is printed.

Example 8: ASCII Value

Output

Enter a character: g
You entered g.
ASCII value is 103.

I/O Multiple Values

Here's how you can take multiple inputs from the user and display them.

Output

Enter integer and then a float: -3
3.4
You entered -3 and 3.400000

Format Specifiers for I/O

As you can see from the above examples, we use

• %d for int
• %f for float
• %lf for double
• %c for char

Here's a list of commonly used C data types and their format specifiers.