Variables and Types — Storing Data in C

C in 100 Seconds, Episode 2

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C is a statically typed language. Every variable has a type, and you declare it up front. No guessing, no auto-detection.

The Four Core Types

int age = 25;
float price = 9.99;
char grade = 'A';
double pi = 3.14159265;

• int — whole numbers. 4 bytes on most systems.
• float — decimal numbers. ~7 digits of precision.
• char — a single character, wrapped in single quotes.
• double — double-precision floating point. ~15 digits of precision.

Printing Variables

Each type has its own format specifier for printf:

printf("Age: %d\n", age);         // %d for int
printf("Price: %.2f\n", price);   // %.2f for float (2 decimals)
printf("Grade: %c\n", grade);     // %c for char
printf("Pi: %.8f\n", pi);         // %.8f for double (8 decimals)

Get the specifier wrong and you get garbage output. C trusts you to match them correctly.

Why Types Matter

C doesn't have a universal "number" type. The type determines how much memory is allocated and how the bits are interpreted. An int and a float storing "the same number" look completely different in memory.

Full Code

#include <stdio.h>

int main() {
  int age = 25;
  float price = 9.99;
  char grade = 'A';
  double pi = 3.14159265;

  printf("Age: %d\n", age);
  printf("Price: %.2f\n", price);
  printf("Grade: %c\n", grade);
  printf("Pi: %.8f\n", pi);

  return 0;
}

Compile and Run

gcc variables.c -o variables
./variables

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Next episode: Format Specifiers — controlling exactly how your data is displayed.

Student code: github.com/GoCelesteAI/c-in-100-seconds/episode02