Strings in C
Strings in C are arrays of characters terminated by a null character ('\0'). Learn how to work with character arrays and string functions.
"In C, a string is just an array of characters with a null terminator at the end - simple yet powerful!"
What is a String in C?
A string in C is a sequence of characters stored in consecutive memory locations and terminated by a null character ('\0'). Strings are essentially character arrays with a special ending marker.
String Declaration and Initialization
Character Array Declaration
// Different ways to declare strings
char str1[20]; // Uninitialized string
char str2[20] = "Hello World"; // Initialized with string literal
char str3[] = "AIVista India"; // Size determined automatically
char str4[6] = {'H', 'e', 'l', 'l', 'o', '\0'}; // Character by characterString Input and Output
#include <stdio.h>
int main() {
char name[50];
// Input a string
printf("Enter your name: ");
scanf("%s", name); // Reads until whitespace
// Output a string
printf("Hello, %s!\n", name);
// Using fgets for full lines
char sentence[100];
printf("Enter a sentence: ");
fgets(sentence, sizeof(sentence), stdin);
printf("You entered: %s", sentence);
return 0;
}String Functions
C provides several built-in string functions in the <string.h> header file.
strlen() - String Length
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "AIVista India";
int length = strlen(str);
printf("String: %s\n", str);
printf("Length: %d characters\n", length);
return 0;
}strcpy() - String Copy
#include <stdio.h>
#include <string.h>
int main() {
char source[] = "Hello World";
char destination[20];
strcpy(destination, source);
printf("Source: %s\n", source);
printf("Destination: %s\n", destination);
return 0;
}strncpy() - Safe String Copy
#include <stdio.h>
#include <string.h>
int main() {
char source[] = "Hello World";
char destination[10];
// Copy only first 9 characters (leaving space for null terminator)
strncpy(destination, source, 9);
destination[9] = '\0'; // Ensure null termination
printf("Source: %s\n", source);
printf("Destination: %s\n", destination);
return 0;
}strcat() - String Concatenation
#include <stdio.h>
#include <string.h>
int main() {
char str1[50] = "Hello";
char str2[] = " World";
strcat(str1, str2);
printf("Concatenated string: %s\n", str1);
return 0;
}strncat() - Safe String Concatenation
#include <stdio.h>
#include <string.h>
int main() {
char str1[20] = "Hello";
char str2[] = " World Program";
// Concatenate only first 6 characters of str2
strncat(str1, str2, 6);
printf("Result: %s\n", str1);
return 0;
}strcmp() - String Comparison
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Apple";
char str2[] = "Banana";
char str3[] = "Apple";
// Compare strings
int result1 = strcmp(str1, str2);
int result2 = strcmp(str1, str3);
printf("strcmp('%s', '%s') = %d\n", str1, str2, result1);
printf("strcmp('%s', '%s') = %d\n", str1, str3, result2);
// Interpretation
if (result1 < 0) {
printf("%s comes before %s\n", str1, str2);
} else if (result1 > 0) {
printf("%s comes after %s\n", str1, str2);
} else {
printf("%s and %s are equal\n", str1, str2);
}
return 0;
}strncmp() - Compare First n Characters
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Hello World";
char str2[] = "Hello Universe";
// Compare only first 5 characters
int result = strncmp(str1, str2, 5);
printf("Comparing first 5 chars: %d\n", result);
if (result == 0) {
printf("First 5 characters are identical\n");
}
return 0;
}String Manipulation Functions
strchr() - Find Character in String
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello World";
char *ptr;
// Find first occurrence of 'o'
ptr = strchr(str, 'o');
if (ptr != NULL) {
printf("Found 'o' at position: %ld\n", ptr - str);
printf("Remaining string: %s\n", ptr);
} else {
printf("Character not found\n");
}
return 0;
}strstr() - Find Substring
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello World Program";
char *ptr;
// Find substring "World"
ptr = strstr(str, "World");
if (ptr != NULL) {
printf("Found 'World' at position: %ld\n", ptr - str);
printf("Found substring: %s\n", ptr);
} else {
printf("Substring not found\n");
}
return 0;
}Custom String Functions
Custom String Length Function
#include <stdio.h>
int my_strlen(char str[]) {
int length = 0;
while (str[length] != '\0') {
length++;
}
return length;
}
int main() {
char str[] = "AIVista India";
printf("Length of '%s' is %d\n", str, my_strlen(str));
return 0;
}Custom String Copy Function
#include <stdio.h>
void my_strcpy(char dest[], char src[]) {
int i = 0;
while (src[i] != '\0') {
dest[i] = src[i];
i++;
}
dest[i] = '\0'; // Add null terminator
}
int main() {
char source[] = "Hello World";
char destination[20];
my_strcpy(destination, source);
printf("Source: %s\n", source);
printf("Destination: %s\n", destination);
return 0;
}String Reversal
#include <stdio.h>
#include <string.h>
void reverse_string(char str[]) {
int start = 0;
int end = strlen(str) - 1;
while (start < end) {
// Swap characters
char temp = str[start];
str[start] = str[end];
str[end] = temp;
start++;
end--;
}
}
int main() {
char str[] = "AIVista India";
printf("Original: %s\n", str);
reverse_string(str);
printf("Reversed: %s\n", str);
return 0;
}Common String Problems
1. Check if String is Palindrome
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int is_palindrome(char str[]) {
int start = 0;
int end = strlen(str) - 1;
while (start < end) {
// Skip non-alphanumeric characters
while (start < end && !isalnum(str[start])) start++;
while (start < end && !isalnum(str[end])) end--;
// Compare characters (case insensitive)
if (tolower(str[start]) != tolower(str[end])) {
return 0; // Not a palindrome
}
start++;
end--;
}
return 1; // Is a palindrome
}
int main() {
char str[] = "A man, a plan, a canal: Panama";
if (is_palindrome(str)) {
printf("'%s' is a palindrome\n", str);
} else {
printf("'%s' is not a palindrome\n", str);
}
return 0;
}2. Count Words in a String
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int count_words(char str[]) {
int count = 0;
int in_word = 0;
for (int i = 0; str[i] != '\0'; i++) {
if (isspace(str[i])) {
in_word = 0;
} else if (in_word == 0) {
in_word = 1;
count++;
}
}
return count;
}
int main() {
char str[] = "Welcome to AIVista India";
printf("String: %s\n", str);
printf("Word count: %d\n", count_words(str));
return 0;
}Advantages of Strings in C
- Simple and efficient for text manipulation
- Direct memory access and control
- Compatible with C's low-level nature
- Rich library of string functions
Limitations and Precautions
- No built-in bounds checking (buffer overflow risk)
- Manual memory management required
- Null termination must be handled carefully
- String operations can be error-prone
Best Practices
- Always allocate enough space for strings (including null terminator)
- Use safe functions like strncpy() and strncat() when possible
- Check for NULL pointers before using string functions
- Include <string.h> header for string functions
- Be aware of buffer overflow vulnerabilities
- Use fgets() instead of gets() for input
Conclusion
Strings are fundamental to C programming and understanding them is crucial for text processing. While C strings can be tricky due to manual memory management, they provide the control and efficiency that makes C powerful. Practice with different string operations to become proficient in string manipulation! 🚀