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:

// 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);

Multiple Inputs

The scanf() function also allow multiple inputs (an integer and a character in the following 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);

Take String Input

You can also get a string entered by the 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);

However, the scanf() function has some limitations: it considers space (whitespace, tabs, etc) as a terminating character, which means that it can only display a single word (even if you type many words). For 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:

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