Strings in C are sequences of characters terminated by a null character (\0).
Unlike other languages, C does not have a dedicated string datatype—strings are implemented using character arrays.

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1. String Declaration in C

Syntax

char string_name[size];

Examples

1.1 Declaring without initialization

char name[20];

1.2 Declaring with initialization

char name[] = "Sagar";

1.3 Using character array form

char name[] = {'S', 'a', 'g', 'a', 'r', '\0'};

1.4 Using scanf to read

char city[20];
scanf("%s", city);   // Stops at space

1.5 Using gets() or fgets()

char sentence[50];
fgets(sentence, sizeof(sentence), stdin);   // Safe method

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2. Common String Functions in C (from <string.h>)

Below are the most frequently used string functions:

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2.1 strlen() – Length of a string

strlen(str);

Example

int len = strlen("Hello");   // Output: 5

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2.2 strcpy() – Copy a string

strcpy(dest, source);

Example:

char a[20], b[20] = "C Language";
strcpy(a, b);   // a = "C Language"

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2.3 strcat() – Concatenate two strings

strcat(str1, str2);

Example:

char name[20] = "Hello ";
strcat(name, "World!");  // Output: Hello World!

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2.4 strcmp() – Compare two strings

Returns:

• 0 → strings are equal
• positive → first is greater
• negative → second is greater

Example:

strcmp("abc", "abd");  // Output: -1

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2.5 strlwr() & strupr() (Compiler-specific)

Convert to lowercase or uppercase.

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3. String Manipulation in C

3.1 Traversing a string

for (int i = 0; str[i] != '\0'; i++) {
    printf("%c\n", str[i]);
}

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3.2 Changing specific characters

char name[] = "Sagar";
name[0] = 'R';  
printf("%s", name);   // Output: Ragar

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3.3 Reversing a string

#include <stdio.h>
#include <string.h>

int main() {
    char str[20] = "Hello";
    int len = strlen(str);

    for(int i = len - 1; i >= 0; i--)
        printf("%c", str[i]);

    return 0;
}

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Program Structure & Storage Classes in C

Storage classes define visibility, lifetime, and scope of variables in C.

The four major storage classes are:

1. Automatic (auto)
2. External (extern)
3. Static (static)
4. (optional) Register (register)

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1. Automatic Variables (auto)

These are local variables inside a function.

Features

• Default storage class for local variables
• Memory allocated when function is called
• Memory released when function ends
• Not accessible outside the function

Example

void demo() {
    auto int a = 10;   // auto is optional
    int b = 20;        // same as auto
}

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2. External Variables (extern)

Used to declare global variables across multiple files.

Features

• Declared outside all functions
• Can be used by any function
• Use extern keyword to access in other files

Example (Single File)

#include <stdio.h>

int x = 10;     // global variable

void display() {
    extern int x;
    printf("%d", x);
}

int main() {
    display();
    return 0;
}

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3. Static Variables (static)

Static variables retain their value even after the function ends.

Features

• Lifetime = entire program
• Scope = local to the block/function
• Value persists between function calls

Example

void counter() {
    static int count = 0;
    count++;
    printf("%d\n", count);
}

int main() {
    counter();  // 1
    counter();  // 2
    counter();  // 3
    return 0;
}

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Summary Table

Storage Class	Scope	Lifetime	Default Value
auto	Local	Within function	Garbage
extern	Global	Entire program	Zero
static (local)	Local	Entire program	Zero
static (global)	File scope	Entire program	Zero

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📚 Citations

🔗 View other articles about C Programming:
https://savanka.com/category/learn/c-programming/

🔗 External C Documentation:
https://www.w3schools.com/c/