c / c-fundamentals
15 mins
C Level 1: Data Types, printf, and scanf
Why This Matters: C requires static type declarations so the compiler knows the exact byte size to allocate in physical RAM.
## Statically Typed Memory in C Every variable in C must be declared with its **type** so the memory allocation size is fixed at compile time. ### Core Data Types & Sizes - `int`: 4 bytes (-2,147,483,648 to 2,147,483,647) — Format: `%d` - `float`: 4 bytes single-precision float — Format: `%f` - `double`: 8 bytes double-precision float — Format: `%lf` - `char`: 1 byte ASCII character — Format: `%c`
MENTAL MODEL & MEMORY LAYOUT
RAM Memory Layout: ┌──────────────────┬──────────────────┐ │ Address 0x1000 │ int age (4 B) │ => 20 ├──────────────────┼──────────────────┤ │ Address 0x1004 │ float gpa (4 B) │ => 3.92 └──────────────────┴──────────────────┘
COMMON PITFALLS TO AVOID
- Using wrong format specifier (e.g. %d for float instead of %f).
- Forgetting the address-of operator `&` in scanf(`%d`, &num).
Reading User Input with scanf
#include <stdio.h>
int main() {
int num;
printf("Enter integer: ");
scanf("%d", &num); // '&' passes memory address
printf("You entered: %d\n", num);
return 0;
}scanf requires the memory address (&num) so it can write directly into the variable's RAM location.
CONCEPT MASTERY CHECKPOINT
Why must you pass `&num` instead of `num` to scanf()?
NEXT RECOMMENDED LESSON
C Level 2: Control Flow & Loops
Challenge: Complete the C code to multiply two integers `a = 6` and `b = 7` and print the result using printf.