Structs in C — Group Your Data

C in 100 Seconds, Episode 23

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Variables are great for single values. But what happens when you need to represent something with multiple properties — like a student with a name, an age, and a GPA? That is where structs come in.

What Is a Struct?

A struct is a custom type that groups different types together under one name. Instead of managing three separate variables, you get one unit.

typedef struct {
  char name[50];
  int age;
  float gpa;
} Student;

typedef lets you use Student directly as a type name. Without it, you would have to write struct Student every time.

Creating and Initializing

Initialize with curly braces — values go in the same order as the members were defined:

Student s = {"Alice", 20, 3.85};

Alice for name, 20 for age, 3.85 for GPA. One line, one variable, all three values.

Accessing Members

Use the dot operator to read any field:

printf("Name: %s\n", s.name);   // Alice
printf("Age:  %d\n", s.age);    // 20
printf("GPA:  %.2f\n", s.gpa);  // 3.85

Modifying Members

Structs are mutable. Assign to any field to change it:

s.age = 21;
printf("Updated age: %d\n", s.age);  // 21

The other fields stay the same. You are only changing what you target.

Why Structs Matter

Structs are the building block of organized data in C:

• Data modeling — represent real-world objects (students, points, records)
• Function parameters — pass a single struct instead of five separate arguments
• Arrays of structs — a list of students, a deck of cards, a table of records
• Pointer to struct — the arrow operator -> unlocks dynamic data structures

Without structs, C programs would be a mess of unrelated variables. With them, your data has shape.

Full Code

#include <stdio.h>

typedef struct {
  char name[50];
  int age;
  float gpa;
} Student;

int main() {
  Student s = {"Alice", 20, 3.85};

  printf("Name: %s\n", s.name);
  printf("Age:  %d\n", s.age);
  printf("GPA:  %.2f\n", s.gpa);

  s.age = 21;
  printf("\nUpdated age: %d\n", s.age);

  return 0;
}

Compile and run:

gcc structs.c -o structs
./structs

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Next episode: Structs and Pointers — the arrow operator and heap-allocated structs.

Student code: github.com/GoCelesteAI/c-in-100-seconds/episode23