Input & Output
C uses two core functions for console I/O: printf() to print output, and scanf() to read input from the keyboard. Both live in stdio.h.
scanf needs the memory address of a variable (using &) so it knows exactly where to store what you type.
💡 Key insight
Forgetting the <code>&</code> before a variable in <code>scanf</code> is the single most common beginner bug in C.
Syntax
syntax
printf("format string", values...);
scanf("format string", &variable);Example
&age passes the address of age so scanf can write the typed value directly into that memory location.
c
#include <stdio.h>
int main() {
int age;
printf("Enter your age: ");
scanf("%d", &age);
printf("You are %d years old.\n", age);
return 0;
}outputEnter your age: 20
You are 20 years old.
Try it yourself
Copy this example into the C compiler and run it — try changing a value and see what happens.