Input & Output

A program that cannot talk to the user is just a silent calculator. C gives you printf for output and scanf for input. These are your program's voice and ears.

printf — Sending Output

printf stands for "print formatted." You give it a string, and it prints it to the console. You can embed format specifiers in the string to print variables.

• %d — int
• %f — float
• %lf — double
• %c — char
• %s — string

scanf — Reading Input

scanf reads input from the user. You pass the format specifier and the address of the variable where the input should be stored. That is why you see the & symbol — it means "address of."

Do not forget the &. Forgetting it is one of the most common C mistakes, and the program will likely crash.

#include 

int main() {
  int age;
  float height;

  printf("Enter your age: ");
  scanf("%d", &age);

  printf("Enter your height in meters: ");
  scanf("%f", &height);

  printf("You are %d years old and %.2f meters tall.\n", age, height);
  return 0;
}