String and pointer in C Programming

String in C Programming

A string is a group of characters.
In C, strings are stored as a character array (e.g., char ch[100];).
Each character occupies an index in the array. For example, the first character is at index 0, the second at index 1, and so on.
The value of a string is essentially a group of characters.
Syntax of string in C:
char ch[100];
It’s clear from the above that a user can store a string if the memory is available.

Accepting and Displaying a String

Example 1: A C program to accept and display a string from the user console.

#include <stdio.h>
#include <conio.h>

void main() {
    char str1[100];
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", str1);
    printf("\n Your entered string = %s", str1);
    getch();
}

%s is used in scanf to read the input string.

Using `gets()` Function

Example 2: Using gets() to accept a string.

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

void main() {
    char str1[100];
    clrscr();
    printf("\n Enter any string: ");
    gets(str1);
    printf("\n Your entered String = %s", str1);
    getch();
}

gets() is a predefined method in C used to accept a string from the user.
It stores the accepted string in the specified array location.
Syntax: gets(variable_name); (e.g., gets(str1);)
gets() is an alternative to scanf(). It accepts an entire line of input, including spaces, until a newline character is encountered.

Alternate example of displaying a string

Example 3: Another way to display a string
c void main() { char str1[100]; clrscr(); printf("\n Enter any string: "); flushall(); gets(str1); printf("\n Your entered string = %s", str1); getch(); }

Finding the Length of a String

Example 4: A C program to accept a string and display its length without using the standard strlen() method.

#include <stdio.h>
#include <conio.h>

void main() {
    int i = 0;
    int len = 0;
    char str[100];
    clrscr();
    printf("\n Enter the string: ");
    flushall();
    gets(str);
    while (str[i] != '\0') {
        len++;
        i++;
    }
    printf("\n The length of the string = %d", len);
    getch();
}

The loop continues until the null character \0 is encountered.

Example 5: Finding the length of a string using the standard strlen() method.

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

void main() {
    int len = 0;
    char str[100];
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", str);
    len = strlen(str);
    printf("\n Length of the String = %d", len);
    getch();
}

strlen() is a standard C function used to find the length of a string.
Syntax: int x = strlen(string);

Copying a String

Example 6: A C program to accept a string from the user and copy it into another array without using the standard method.

#include <stdio.h>
#include <conio.h>

void main() {
    char str1[100];
    char str2[100];
    int i = 0;
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", str1);
    while (str1[i] != '\0') {
        str2[i] = str1[i];
        i++;
    }
    str2[i] = '\0';
    printf("\n Copied String = %s", str2);
    getch();
}

Example 7: A C program to copy a string into another array using the standard method strcpy().

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

void main() {
    char str1[100];
    char str2[100];
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", &str1);
    strcpy(str2, str1);
    printf("\n Copied string = %s", str2);
    getch();
}

strcpy(destination, source) copies the string from source to destination.

String Concatenation

Example 8: A C program to accept two strings from the user and copy them into a third character array.

#include <stdio.h>
#include <conio.h>

void main() {
    char str1[100];
    char str2[100];
    char str3[100];
    int i = 0, j = 0, k = 0;
    clrscr();
    printf("\n Enter first string: ");
    scanf("%s", &str1);
    printf("\n Enter second string: ");
    scanf("%s", &str2);
    while (str1[i] != '\0') {
        str3[k] = str1[i];
        i++;
        k++;
    }
    while (str2[j] != '\0') {
        str3[k] = str2[j];
        j++;
        k++;
    }
    str3[k] = '\0';
    printf("\n Merged String = %s", str3);
    getch();
}

Example 9: A C program to concatenate the second string at the end of the first string using the standard method strcat().

#include <stdio.h>
#include <conio.h>

void main() {
    char str1[100];
    char str2[100];
    clrscr();
    printf("\n Enter the first string: ");
    scanf("%s", &str1);
    printf("\n Enter the second string: ");
    scanf("%s", &str2);
    strcat(str1, str2);
    printf("\n Concatenated String = %s", str1);
    getch();
}

strcat(destination, source) concatenates the string source to the end of the destination string.

Example 10: A C program to copy the second string at the end of the first string using both strcpy() and strcat().

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

void main() {
    char str1[100];
    char str2[100];
    char str3[100];
    clrscr();
    printf("\n Enter the first string: ");
    scanf("%s", &str1);
    printf("\n Enter the second string: ");
    scanf("%s", &str2);
    strcpy(str3, str1);
    strcat(str3, str2);
    printf("\n Merged string = %s", str3);
    getch();
}

String Reversal

Example 12: A C program to accept a string from the user and display the reverse of that string using the standard method strrev().

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

void main() {
    char str1[100];
    clrscr();
    printf("\n Enter the 1st string: ");
    scanf("%s", &str1);
    strrev(str1);
    printf("\n Reverse of String = %s", str1);
    getch();
}

Example 13: String reversal without using standard method.

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

void main() {
    char str1[100];
    int i = 0;
    int len = 0;
    clrscr();
    printf("\n Enter the 1st string: ");
    scanf("%s", &str1);len = strlen(str1);
printf("\n Reverse of the String is ");

for (i = len - 1; i &gt;= 0; i--)
    printf("%c", str1[i]);

getch();
}

String Comparison

strcmp() is a standard method in C used to compare two strings.
If the two strings are equal, it returns 0.
If the first string is greater than the second string, it will return a positive value.
If the first string is less than the second string, it will return a negative value.
Syntax: strcmp(string1, string2);

String Comparison Examples

Example 14: A C program to accept two strings from the user and check whether the strings are equal or not.

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

void main() {
    char str1[100], str2[100];
    clrscr();
    printf("\n Enter first string: ");
    scanf("%s", str1);
    printf("\n Enter second string: ");
    scanf("%s", str2);
    if (strcmp(str1, str2) == 0)
        printf("\n Two Strings are equal");
    else
        printf("\n Two strings are not equal");
    getch();
}

Example 15: A C program to accept two strings from the user and display the greater string.

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

void main() {
    char str1[100], str2[100];
    clrscr();
    printf("\n Enter first string: ");
    scanf("%s", str1);
    printf("\n Enter second string: ");
    scanf("%s", str2);if (strcmp(str1, str2) &gt; 0)
    printf("\n First string is greater");
else
    printf("\n Second string is greater");
getch();
}

Considering Space in String Input

To consider spaces in string input, the following methods can be used in C programming.
1. gets()
2. fgets(): This is also a standard method in C programming that is used to consider space in string format.
  - Syntax: fgets(str1, 100, stdin);
3. scanf(): This is a standard method available in stdio.h and is used to read all characters in a string, including spaces.
  - Syntax: scanf("%[^\n]%*c", str1);

String and Functions

Example 17: A C program to accept a string from the user and display that string using a function.

#include <stdio.h>
#include <conio.h>

void display(char[]);

void main() {
    char str1[100];
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", &str1);
    display(str1);
    getch();
}

void display(char str1[100]) {
    printf("\n String from main function = %s", str1);
}

Example 18: Copy string into another string using function

#include <stdio.h>
#include <conio.h>
void display(char[]);
void main()
{
    char str1[100];
    char str2[100];
    int i = 0;
    clrscr();
    printf("\n Enter the string: ");
    scanf("%s", str1);
    display(str1);
    getch();
}

void display(char str1[100])
{
    char str2[100];
    int i = 0;
    while (str1[i] != '\0')
    {
        str2[i] = str1[i];
        i++;
    }
    str2[i] = '\0';
    printf("\n Copied string = %s", str2);getch();
}

Example 19:

#include <stdio.h>
#include <conio.h>
void main()
{
    char str1[100];
    char str2[100];
    int ch = 0;
    int i = 0;
    int len = 0;
    clrscr();
    printf("\n Enter any string: ");
    scanf("%s", str1);printf("\n 1. Display length of the string\n ");
printf("\n 2. Copy one string to another char string\n ");
printf("\n Enter your choice: ");
scanf("%d", &amp;ch);
switch (ch)
{
case 1:
{
    while (str1[i] != '\0')
    {
        len++;
        i++;
    }
    printf("\n The length of the string = %d", len);
}
break;
case 2:
{
    while (str1[i] != '\0')
    {
        str2[i] = str1[i];
        i++;
    }
    str2[i] = '\0';
    printf("\n Copied string = %s", str2);
}
break;
}
getch();
}

Pointers in C

A pointer is a variable that holds the memory address of another variable.
Pointers are represented with the * symbol.
When variables are stored in memory, they have specific addresses.
Using a pointer, you can access and manipulate the data stored at that memory address.
The address of operator & is used to get the address of a variable.
Dereferencing a pointer (using *) allows you to access the value stored at the pointer's address.
This is also known as "call by reference”.
Sending the address of a variable to a function allows the function to modify the original variable.

Types of Pointers:

Integer Pointer: Points to an integer variable.
Array Pointer: Points to an array.
Structure Pointer: Points to a structure.
Function Pointer: Points to a function.
Null Pointer: A pointer that does not point to any valid memory location and is often represented as (void *)0.
Void Pointer: A pointer that can point to any type of variable. The syntax is (void *).
Near Pointer: Can only point to memory locations within the current segment.
Far Pointer: Can point to memory locations outside the current segment.
Constant Pointer: The value of the pointer does not change even if the memory location of pointer is changed. (using const outside)

Issues with Pointers

Wild Pointer: A pointer that has not been initialized and points to an unknown memory location. Using a wild pointer can cause the program to crash or behave unpredictably.
Dangling Pointer: A pointer that points to a memory location that has already been freed or deallocated.
Hanging Pointer: A pointer that points to a memory location that is no longer being used, but the memory is still occupied, and calls dangling pointer.

Pointer Example

#20: Using Pointer

//Write a C program to accept any number & display that no using pointer
#include <stdio.h>
#include <conio.h>
void display(int *);
void main()
{
    int a = 0;
    clrscr();
    printf("\n Enter any number: ");scanf("%d", &amp;a);
display(&amp;a);

getch();
}
void display(int *x)
{
    printf("\n The no from main function = %d", *x);
}

Call by reference

#21: call by reference

// Write a C program to accept two no from user & display their addition by call by reference(Pointer)
#include <stdio.h>
#include <conio.h>
void add(int *, int *);
void main()
{
    int a = 0;
    int b = 0;
    clrscr();
    printf("\n Enter the 1st number: ");
    scanf("%d", &a);
    printf("\n Enter the 2nd number: ");
    scanf("%d", &b);
    add(&a, &b);
    getch();
}
void add(int *x, int *y)
{
    int ans = *x + *y;printf("\n The Addition = %d", ans);
}

Arithmetic Operations.

#22: addition using pointer

//Write a program to accept two no from uses & display their add " using pointes :-
#include <stdio.h>
#include <conio.h>
void main()
{
    int a = 0;
    int b = 0;
    int *a1 = 0;
    int *a2 = 0;
    int ans = 0;
    clrscr();
    printf("\n Enter the 1st number: ");
    scanf("%d", &a);
    printf("\n Enter the 2nd number: ");
    scanf("%d", &b);
    a1 = &a;
    a2 = &b;
    ans = (*a1) + (*a2);
    printf("\n Addition: %d", ans);
    getch();
};

#23: subtraction using pointer

//Subtraction using  Pointer
#include <stdio.h>
#include <conio.h>
void main()
{
    int a = 0;
    int b = 0;
    int *a1 = 0;
    int *b1 = 0;
    clrscr();
    printf("\n Enter 1st za (no: ");
    scanf("%d", &a);
    printf("\n Enter 2nd za nu: ");
    scanf("%d", &b);
    a1 = &a;
    b1 = &b;
    int ans = (*a1) - (*b1);
    printf("\n Subtraction = %d", ans);
    getch();
}

Swapping Numbers

#24: Swapping of two no.

#include <stdio.h>
#include <conio.h>
void main()
{
    int a = 0;
    int b = 0;
    int temp = 0;
    clrscr();
    printf("\n Enter 1st nu : ");
    scanf("%d", &a);
    printf("\n Enter 2st nu: ");
    scanf("%d", &b);
    printf("\n The values before, scorffing. \n");
    printf("\n first no =%d", a);
    printf("\n Secad ra =%d", b);
    int *a1 = &a;
    int *b1 = &b;
    temp = *a1;
    *a1 = *b1;
    *b1 = temp;printf("\n The values after swraffing la \n ");
printf("\n First za = %d", a);
printf("\n Secad no =%d", b);

getch();
};

Reverse order & Even/Odd

#25: Reverse
```c
#include
#include
//Write a c program to accept one number from uses
//& display the reverse of that nes by using call by reference.
void reverse(int *);
void main()
{
clrscr();
int a;
printf("\n Enter any number: ");
scanf("%d", &a);
reverse(&a);
getch();
}
void reverse(int *n)
{
int rem = 0;
int rev = 0;
while ((n) != 0) { rem = (n) % 10;
rev = (rev * 10) + rem;
(n) = (n) / 10;
}
printf("\n Reverse of ther not = %d ", rev);
};

*   **#26**: Even/Odd using pointer

    ```c

    //Write wheather no. is even & odd using pointer
    #include <stdio.h>
    #include <conio.h>
    void main()
    {
        int z = 0;
        int *a = 0;
        clrscr();
        printf("\n Entre any number: ");
        scanf("%d", &z);
        a = &z;
        if ((*a % 2) == 0)
        {
            printf("\n This z= is even\n ");
        }
        else
        {
            printf("\n This z= is odd ");
        }
        getch();
    };
    ```

## More Pointer examples

*   **#27**:  Write code to display the sum of the individual digits of input numbers.

c
//Pas Accept any number from uses
//add & disfley that digits of the number
// from the console & display the add
#include
#include
// #include
void digitadd(int *);
void main()
{
clrscr();
int a = 0;
printf("\n Enter any number: ");
scanf("%d", &a);
digitadd(&a);
getch();
}

void digitadd(int *no)
{
    int rem = 0;
    int sum = 0;
    while ((*no) != 0)
    {
        rem = (*no) % 10;
        sum = sum + rem;

        *no = (*no) / 10;
    }

    printf("\n Add of the digits = %d\n