C scanf()

scanf reads what a person types and stores it in a variable, like a teacher writing down your answer. You tell it what type to expect and where to put it.

In this page:

What is scanf()?
Reading an Integer
Reading a Character
Reading a Floating-Point Value
Reading Multiple Values Together

Syntax

scanf("%specifier", &variable_name);

What is scanf()?

scanf ("scan formatted") reads input the user types at the keyboard and stores it into your program's variables, making it the standard way a C program becomes interactive instead of just running with hardcoded data.

Example: What is scanf()?

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	int age;
	sscanf("25", "%d", &age);
	// Print formatted text to the screen
	printf("%d", age);
	// Return 0 to signal that the program finished successfully
	return 0;
}

Reading an Integer

Reading an int requires the %d specifier and an ampersand before the variable name (scanf("%d", &age);), because scanf needs the variable's memory address to write the value into -- passing the variable itself instead of its address is a classic beginner bug.

Example: Reading an Integer

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	int age;
	sscanf("25", "%d", &age);
	// Print formatted text to the screen
	printf("%d", age);
	// Return 0 to signal that the program finished successfully
	return 0;
}

Reading a Character

Reading a single character with %c is sensitive to leftover whitespace or newline characters sitting in the input buffer from a previous scanf call, which can cause the next read to silently grab a space instead of the character you expect.

Example: Reading a Character

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	char grade;
	sscanf("A", "%c", &grade);
	// Print formatted text to the screen
	printf("%c", grade);
	// Return 0 to signal that the program finished successfully
	return 0;
}

Reading a Floating-Point Value

%f reads a decimal number into a float variable, letting your program accept things like measurements or prices directly from user input rather than only working with values baked into the source code.

Example: Reading a Floating-Point Value

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	float price;
	sscanf("19.99", "%f", &price);
	// Print formatted text to the screen
	printf("%.2f", price);
	// Return 0 to signal that the program finished successfully
	return 0;
}

Reading Multiple Values Together

A single scanf call can read several values at once, like scanf("%d %f", &count, &price);, as long as the format string lists each specifier in the same order as the variables and matching addresses that follow.

Example: Reading Multiple Values Together

// Include standard input/output (printf, scanf)
#include <stdio.h>
// Program execution starts in main()
int main() {
	int count;
	float price;
	sscanf("3 9.99", "%d %f", &count, &price);
	// Print formatted text to the screen
	printf("%d %.2f", count, price);
	// Return 0 to signal that the program finished successfully
	return 0;
}

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