> ## Documentation Index
> Fetch the complete documentation index at: https://learn.acadlink.app/llms.txt
> Use this file to discover all available pages before exploring further.

# String Manipulation Functions

> Built-in string functions from string.h in C

# String Manipulation Functions in C

C provides built-in library functions to work with strings — declared in **`<string.h>`**. These let you copy, concatenate, compare, measure, and reverse strings without writing the logic yourself.

```c theme={null}
#include <string.h>
```

***

## 1. `strlen()` — Get the Length

Returns the number of characters in a string, **excluding** the null terminator `'\0'`.

```c theme={null}
#include <stdio.h>
#include <string.h>

int main() {
    char name[20] = "Vishal";
    int len = strlen(name);
    printf("Length = %d", len);   // Output: 6
    return 0;
}
```

***

## 2. `strcpy()` — Copy a String

Copies the content of one string into another. The destination must be large enough.

```c theme={null}
#include <stdio.h>
#include <string.h>

int main() {
    char str1[20] = "Hello";
    char str2[20];
    strcpy(str2, str1);
    printf("Copied: %s", str2);   // Output: Hello
    return 0;
}
```

***

## 3. `strcat()` — Concatenate Strings

Appends one string to the end of another. The destination must have enough space.

```c theme={null}
#include <stdio.h>
#include <string.h>

int main() {
    char str1[30] = "Hello ";
    char str2[10] = "World!";
    strcat(str1, str2);
    printf("%s", str1);   // Output: Hello World!
    return 0;
}
```

***

## 4. `strcmp()` — Compare Strings

Compares two strings character by character:

* Returns `0` if both strings are **equal**
* Returns `> 0` if the first string is **greater**
* Returns `< 0` if the second string is **greater**

```c theme={null}
#include <stdio.h>
#include <string.h>

int main() {
    char str1[20] = "abc";
    char str2[20] = "abd";
    int result = strcmp(str1, str2);
    if (result == 0)
        printf("Strings are equal");
    else
        printf("Strings are not equal");
    return 0;
}
// Output: Strings are not equal
```

***

## 5. `strrev()` — Reverse a String

Reverses the string in place. Available in Turbo C / MinGW compilers — **not in all compilers** (not part of the C standard).

```c theme={null}
#include <stdio.h>
#include <string.h>

int main() {
    char str[20] = "Future";
    printf("Reversed: %s", strrev(str));
    return 0;
}
// Output: Reversed: erutuF
```

**For portability**, write your own reverse:

```c theme={null}
#include <stdio.h>
#include <string.h>

void reverseStr(char str[]) {
    int n = strlen(str);
    for (int i = 0; i < n / 2; i++) {
        char temp = str[i];
        str[i] = str[n - 1 - i];
        str[n - 1 - i] = temp;
    }
}
```

***

## Quick Reference

All functions below need `#include <string.h>`.

| Function         | Description                        |
| ---------------- | ---------------------------------- |
| `strlen(s)`      | Length of string (excludes `'\0'`) |
| `strcpy(d, s)`   | Copy `s` into `d`                  |
| `strcat(d, s)`   | Append `s` to end of `d`           |
| `strcmp(s1, s2)` | Compare two strings                |
| `strrev(s)`      | Reverse string (compiler-specific) |
| `strupr(s)`      | Convert to uppercase (Turbo C)     |
| `strlwr(s)`      | Convert to lowercase (Turbo C)     |