How to Declare Structure in C: Syntax and Examples

In C, you declare a structure using the struct keyword followed by the structure name and a block of member variables inside braces. For example, struct Person { int age; char name[50]; }; defines a structure named Person with two members.

Syntax

A structure in C is declared using the struct keyword, followed by the structure name and a block containing member declarations inside curly braces. Each member has a type and a name, separated by semicolons. The declaration ends with a semicolon.

• struct: keyword to define a structure
• StructureName: the name you give to the structure
• { ... }: braces containing member variables
• Members: variables inside the structure with types
• ;: semicolon ends the declaration

c

struct StructureName {
    type member1;
    type member2;
    // more members
};

Example

This example shows how to declare a structure named Person with two members: age (an integer) and name (a string). It also shows how to create a variable of this structure and print its values.

c

#include <stdio.h>

struct Person {
    int age;
    char name[50];
};

int main() {
    struct Person person1;

    person1.age = 30;
    // Copying string safely
    snprintf(person1.name, sizeof(person1.name), "%s", "Alice");

    printf("Name: %s\n", person1.name);
    printf("Age: %d\n", person1.age);

    return 0;
}

Output

Name: Alice
Age: 30

Common Pitfalls

Common mistakes when declaring structures in C include:

• Forgetting the semicolon ; after the closing brace of the structure declaration.
• Not using the struct keyword when declaring variables of the structure type (unless using typedef).
• Incorrectly copying strings into character arrays inside structures (use strcpy or snprintf instead of direct assignment).

c

/* Wrong: Missing semicolon after structure declaration */
struct Person {
    int age;
    char name[50]
}  // <-- Missing semicolon here

/* Correct: */
struct Person {
    int age;
    char name[50];
};

Quick Reference

Remember these tips when working with structures in C:

• Always end the structure declaration with a semicolon.
• Use struct StructureName variable; to declare variables.
• Use typedef to simplify variable declarations if desired.
• Access members with the dot operator: variable.member.

Key Takeaways

Use the struct keyword followed by braces and members to declare a structure.

Always end the structure declaration with a semicolon to avoid syntax errors.

Declare variables with struct StructureName variable; unless using typedef.

Access structure members using the dot operator, like variable.member.

Use safe string functions like snprintf to assign strings to character arrays in structures.