C Language Input/Output (I/O)/O)

In this tutorial, you will learn how to use the scanf() function to obtain input from the user and use the printf() function to display output to the user.

C Language Output

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

Example1C Language output

#include <stdio.h>　　　　
int main()
{　
　　　　//Print the string inside the quotes
　　　　printf("C　Programming");
　　　　return 0;
}

Output result

C　Programming

How does this program work?

• All valid C programs must include the main() function. The code starts executing from the beginning of the main() function.

• printf() is a library function to format output sent to the screen. The function will print the string inside the quotes.

• To use the printf() function in our program, we need to include the stdio.h header file using the #include <stdio.h> statement.

• return 0; The statement in the main() function is the program's 'exit status'. It is optional.

Example2Integer output

#include <stdio.h>
int main()
{
　　　　int　testInteger　=　5;
　　　　printf("Number　=　%d",　testInteger);
　　　　return 0;
}

Output result

Number　=　5

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

Example3Single precision floating point and double precision floating point number output

#include <stdio.h>
int main()
{
　　　　float　number1　=　13.5;
　　　　double　number2　=　12.4;
　　　　printf("number1　=　%f\n",　number1);
　　　　printf("number2　=　%lf",　number2);
　　　　return 0;
}

Output result

number1　=　13.500000
number2　=　12.400000

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

Example4Printing characters

#include <stdio.h>
int main()
{
　　　　char　chr　=　'a';　　　　
　　　　printf("character　=　%c.",　chr);　　
　　　　return 0;
}

Output result

character　=　a

To print char, we use the %c format specifier.

C Language input

In C programming, scanf() is one of the commonly used functions to accept input from the user. This scanf() function reads formatted input from the standard input (such as the keyboard).

Example5Integer input/Output

#include <stdio.h>
int main()
{
　　　　int　testInteger;
　　　　printf("Enter a number:　");
　　　　scanf("%d",　&testInteger);　　
　　　　printf("Number　=　%d",testInteger);
　　　　return 0;
}

Output result

Enter a number:　4
Number　=　4

Here, we use the format specifier %d inside the scanf() function to receive the user's input integer value. When the user enters an integer, it will be stored in the testInteger variable.

Note that scanf() uses &testInteger inside. This is because &testInteger gets the address testInteger, and the user input value is stored at that address.

Example6Single precision floating point and double precision floating point number input/Output

#include <stdio.h>
int main()
{
　　　　float num1;
　　　　double num2;
　　　　printf("Enter a number:");
　　　　scanf("%f", &num1);
　　　　printf("Enter another number:");
　　　　scanf("%lf", &num2);
　　　　printf("num1　= %f\n", num1);
　　　　printf("num2　= %lf, num2);
　　　　return 0;
}

Output result

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

Float and double are represented by %f and %lf format specifiers.

Example7: C character I / O

#include <stdio.h>
int main()
{
　　　　char chr;
　　　　printf("Enter a character:");
　　　　scanf("%c", &chr);　　　　　
　　　　printf("You entered %c.", chr);　　
　　　　return 0;
}

Output result

Enter a character: g
You entered g.

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

When we use %c text format to display the value, the entered character will be displayed. If %d is used to display a character, its ASCII value will be printed out.

Example8ASCII value

#include <stdio.h>
int main()
{
　　　　char chr;
　　　　printf("Enter a character:");
　　　　scanf("%c", &chr);　　　　　
　　　　//When using %c, a character will be displayed
　　　　printf("You entered %c.\n", chr);　　
　　　　//When using %d, display the ASCII value
　　　　printf("ASCII value %d.", chr);　　
　　　　return 0;
}

Output result

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

Multiple value input/output (I/O)

This is an example of how to get multiple inputs from the user and display them.

#include <stdio.h>
int main()
{
　　　　int a;
　　　　float b;
　　　　printf("Enter an integer, then enter a floating-point number:");
　　
　　　　//Accept multiple inputs
　　　　scanf("%d%f", &a, &b);
　　　　printf("You entered %d and %f", a, b);　　
　　　　return 0;
}

Output result

Enter an integer, then enter a floating-point number:　-3
3.4
You entered　-3　and　3.400000

I / The format specifier for O

From the above examples, we can see that we use

• %d corresponds to int

• %f corresponds to float

• %lf corresponds to double

• %c corresponds to char

This is a list of commonly used C data types and their format specifiers.