How to Initialize String in C: Syntax and Examples

In C, you can initialize a string by declaring a character array with double quotes like char str[] = "Hello"; or by using a pointer to a string literal like char *str = "Hello";. The first creates a modifiable array, while the second points to a read-only string.

Syntax

There are two common ways to initialize strings in C:

• Character array: char str[] = "text"; creates an array with space for the string and a null terminator.
• Pointer to string literal: char *str = "text"; points to a fixed string stored in read-only memory.

The null terminator \0 marks the end of the string in both cases.

c

char str1[] = "Hello";
char *str2 = "World";

Example

This example shows how to initialize strings using both methods and print them.

c

#include <stdio.h>

int main() {
    char str1[] = "Hello";  // modifiable array
    char *str2 = "World";  // pointer to string literal

    printf("str1: %s\n", str1);
    printf("str2: %s\n", str2);

    // Modifying str1 is allowed
    str1[0] = 'h';
    printf("Modified str1: %s\n", str1);

    // Modifying str2 is undefined behavior and should be avoided
    return 0;
}

Output

str1: Hello
str2: World
Modified str1: hello

Common Pitfalls

Common mistakes when initializing strings in C include:

• Trying to modify a string literal through a pointer, which causes undefined behavior.
• Not leaving space for the null terminator when declaring character arrays.
• Using uninitialized character arrays without setting values.

Always ensure arrays have enough space and avoid changing string literals.

c

#include <stdio.h>

int main() {
    // Wrong: modifying string literal causes crash or undefined behavior
    char *str = "Hello";
    // str[0] = 'h'; // Do NOT do this!

    // Right: use character array to modify string
    char str2[] = "Hello";
    str2[0] = 'h';
    printf("%s\n", str2);
    return 0;
}

Output

hello

Quick Reference

Method	Syntax	Modifiable	Notes
Character array	char str[] = "text";	Yes	Array stores string with null terminator
Pointer to literal	char *str = "text";	No	Points to read-only memory, do not modify

Key Takeaways

Use character arrays to create modifiable strings with space for the null terminator.

Use pointers to string literals only for read-only strings and avoid modifying them.

Always ensure strings end with a null terminator '\0' to mark their end.

Modifying string literals causes undefined behavior and should be avoided.

Initializing strings properly prevents common bugs and crashes in C programs.