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Introduction to Strings

1. An array of characters is called a string.

2. Strings are used to manipulate text or sentences.

3. Real-world applications include:

- Spell checkers

- Spam filters

- Search engines

- Bioinformatics

- Digital forensics

Strings in C

1. Strings are terminated by a null character '\\0'.

2. Syntax:

\n   char string_name[] = \"text\";\n\n   ```\n\n3\\. Example:\n\n```c\n\n   char greeting[] = \"Hello World\";\n\n   ```\n\n   - The null character is added automatically\n\n   - This is called a string constant\n\nAlternative declarations:\n\n```c\n\nchar greeting[12] = {'H','e','l','l','o',' ','W','o','r','l','d','\\0'};\n\n

\nchar name[size];  // Can store size-1 characters + null\n\n

Memory Representation

Example:

\nchar word[] = \"Hello\";\n\n

| Index | 0 | 1 | 2 | 3 | 4 | 5 |

|-------|---|---|---|---|---|---|

| Char | H | e | l | l | o | \\0|

| Address|1000|1001|1002|1003|1004|1005|

\n
Each character occupies 1 byte
\n
\n
word[1] accesses 'e' at address 1001
\n

Reading Strings

1. Using scanf()

\nscanf(\"%s\", str);\n\n

\n
Stops reading at whitespace
\n
\n
No & needed for strings
\n
\n
Null character automatically appended
\n

2. Using gets() (Deprecated)

\ngets(str);\n\n

\n
Reads entire line including spaces
\n
\n
Dangerous - no buffer overflow protection
\n
\n
Avoid using in new code
\n

3. Using fgets()

\nfgets(str, size, stdin);\n\n

\n
Safer than gets()
\n
\n
Reads up to size-1 characters
\n
\n
Includes newline character
\n

4. Using getline() (Recommended)

\nsize_t getline(char **lineptr, size_t *n, FILE *stream);\n\n

Example:

\n#include <stdio.h>\n\n#include <stdlib.h>\n\nint main() {\n\n    char *buffer = NULL;\n\n    size_t size = 0;\n\n    ssize_t chars_read;\n\n    printf(\"Enter string: \");\n\n    chars_read = getline(&buffer, &size, stdin);\n\n    if(chars_read != -1) {\n\n        printf(\"You entered: %s\", buffer);\n\n        printf(\"Buffer size: %zu\\n\", size);\n\n    }\n\n    free(buffer);\n\n    return 0;\n\n}\n\n

\n
Dynamically allocates memory
\n
\n
Handles any input size safely
\n

5. Using getdelim()

\ngetdelim(&buffer, &size, delimiter, stream);\n\n

\n
General version of getline()
\n
\n
Can specify any delimiter character
\n

6. Using getchar()

\nchar ch;\n\nint i = 0;\n\nwhile((ch = getchar()) != '\\n') {\n\n    str[i++] = ch;\n\n}\n\nstr[i] = '\\0';\n\n

\n
Reads one character at a time
\n
\n
Must manually add null terminator
\n

Printing Strings

1. Using printf()

\nprintf(\"%s\", str);\n\n

\n
Most flexible method
\n
\n
Supports formatting
\n

2. Using puts()

\nputs(str);\n\n

\n
Automatically adds newline
\n
\n
Simple but less flexible
\n

3. Using putchar()

\nfor(int i=0; str[i]!='\\0'; i++) {\n\n    putchar(str[i]);\n\n}\n\n

Prints one character at a time

4. Using sprintf()

\nchar buffer[100];\n\nsprintf(buffer, \"Formatted %s\", str);\n\n

\n
Stores formatted output in buffer
\n
\n
Risk of buffer overflow
\n

String Operations

Calculating String Length

Method 1: Manual Calculation

\nint length = 0;\n\nwhile(str[length] != '\\0') {\n\n    length++;\n\n}\n\n

Method 2: Using strlen()

\n#include <string.h>\n\nint len = strlen(str);\n\n

Example Programs:

\n// Using gets() (not recommended)\n\n#include <stdio.h>\n\nint main() {\n\n    char str[100];\n\n    printf(\"Enter string: \");\n\n    gets(str);  // Warning: deprecated\n\n    printf(\"Length: %d\\n\", strlen(str));\n\n    return 0;\n\n}\n\n// Using fgets()\n\n#include <stdio.h>\n\n#include <string.h>\n\nint main() {\n\n    char str[100];\n\n    printf(\"Enter string: \");\n\n    fgets(str, sizeof(str), stdin);\n\n    str[strcspn(str, \"\\n\")] = '\\0';  // Remove newline\n\n    printf(\"Length: %zu\\n\", strlen(str));\n\n    return 0;\n\n}\n\n

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