C scanf()

In this page:

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

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 <stdio.h>
int main() {
	int age;
	sscanf("25", "%d", &age);
	printf("%d", age);
	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 <stdio.h>
int main() {
	int age;
	sscanf("25", "%d", &age);
	printf("%d", age);
	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 <stdio.h>
int main() {
	char grade;
	sscanf("A", "%c", &grade);
	printf("%c", grade);
	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 <stdio.h>
int main() {
	float price;
	sscanf("19.99", "%f", &price);
	printf("%.2f", price);
	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 <stdio.h>
int main() {
	int count;
	float price;
	sscanf("3 9.99", "%d %f", &count, &price);
	printf("%d %.2f", count, price);
	return 0;
}

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