C User Input
User Input
You have already learned that printf() is used to output values in C.
To get user input, you can use the scanf() function:
Example
Output a number entered by the user:
// Create an integer variable that will store the number we get from the user
int myNum;
// Ask the user to type a number
printf("Type a number:
\n");
// Get and save the number the user types
scanf("%d", &myNum);
// Output the number the user typed
printf("Your number is: %d", myNum);
Run example »
The scanf() function takes two arguments: the format specifier of the variable (%d in the example above) and the memory address of the variable (&myNum).
The & is called the reference operator. It gives the memory address of myNum, so scanf() knows where to store the number.
Tip: You will learn more about memory addresses in the next chapter, and about functions later in this tutorial.
Multiple Inputs
The scanf() function also allows multiple
inputs (an integer and a character in the following example):
Example
// Create an int and a char variable
int myNum;
char myChar;
// Ask the user to type a number AND a character
printf("Type a number AND
a character and press enter: \n");
// Get and save the number AND
character the user types
scanf("%d %c", &myNum, &myChar);
// Print
the number
printf("Your number is: %d\n", myNum);
// Print the
character
printf("Your character is: %c\n", myChar);
Run example »
Take String Input
You can also get a string entered by the user:
Example
Output the name of a user:
// Create a string
char firstName[30];
// Ask the user to input some
text
printf("Enter your first name: \n");
// Get and save the text
scanf("%s", firstName);
// Output the text
printf("Hello %s",
firstName);
Run example »
Note: When you use scanf() with a string, the array must be big enough for the text (we used 30, which is enough for most first names).
You also do not use the reference operator (&) with strings, because the name of an array already gives its memory address.
However, the scanf() function has some limitations: it stops reading at the first whitespace (a space, a tab or a new line), which means that it can only read a single word (even if you type many words). For example:
Example
char fullName[30];
printf("Type your full name: \n");
scanf("%s", fullName);
printf("Hello %s",
fullName);
// Type your full name: John Doe
// Hello John
From the example above, you would expect the program to print "John Doe", but it only prints "John".
That's why, when working with strings, we often use the fgets() function to
read a line of text. Note that you must include the following
arguments: the name of the string variable, sizeof(string_name), and stdin (standard input, which is usually the keyboard):
Example
char fullName[30];
printf("Type your full name: \n");
fgets(fullName, sizeof(fullName), stdin);
printf("Hello %s",
fullName);
// Type your full name: John Doe
// Hello John Doe
Run example »
Use the scanf() function to get a single word as input, and use fgets() for multiple words.
