Introduction
String handling in C involves working with sequences of characters stored as arrays. Since C doesn’t have a built-in string data type, strings are represented as null-terminated character arrays. Understanding string manipulation is essential for text processing, user input handling, and many practical programming tasks.
Key Concepts
Null Terminator: Strings end with ‘\0’ character Character Array: Strings are arrays of char type String Literals: Text enclosed in double quotes String Functions: Library functions in string.h for manipulation
String Declaration and Initialization
Different Ways to Declare Strings
#include <stdio.h>
#include <string.h>
int main() {
// Method 1: Character array with size
char str1[20];
// Method 2: Initialize with string literal
char str2[] = "Hello World";
// Method 3: Character array with explicit initialization
char str3[] = {'H', 'e', 'l', 'l', 'o', '\0'};
// Method 4: Fixed size with initialization
char str4[50] = "Programming";
// Method 5: String pointer (read-only)
char *str5 = "Constant String";
printf("str2: %s\n", str2);
printf("str3: %s\n", str3);
printf("str4: %s\n", str4);
printf("str5: %s\n", str5);
return 0;
}Basic String Input/Output
Reading and Printing Strings
#include <stdio.h>
int main() {
char name[50];
char city[30];
printf("Enter your name: ");
scanf("%s", name); // Reads until whitespace
printf("Enter your city: ");
getchar(); // Consume newline left by scanf
fgets(city, sizeof(city), stdin); // Reads entire line
printf("Hello %s from %s", name, city);
return 0;
}Safe String Input
#include <stdio.h>
#include <string.h>
int main() {
char input[100];
printf("Enter a sentence: ");
if (fgets(input, sizeof(input), stdin) != NULL) {
// Remove newline if present
size_t len = strlen(input);
if (len > 0 && input[len-1] == '\n') {
input[len-1] = '\0';
}
printf("You entered: %s\n", input);
}
return 0;
}Essential String Functions
String Length (strlen)
#include <stdio.h>
#include <string.h>
int main() {
char text[] = "Programming";
printf("String: %s\n", text);
printf("Length: %zu\n", strlen(text));
// Manual length calculation
int length = 0;
while (text[length] != '\0') {
length++;
}
printf("Manual length: %d\n", length);
return 0;
}String Copy (strcpy, strncpy)
#include <stdio.h>
#include <string.h>
int main() {
char source[] = "Hello World";
char dest1[50];
char dest2[50];
// Copy entire string
strcpy(dest1, source);
printf("Copied string: %s\n", dest1);
// Copy first n characters
strncpy(dest2, source, 5);
dest2[5] = '\0'; // Manually add null terminator
printf("Partial copy: %s\n", dest2);
return 0;
}String Concatenation (strcat, strncat)
#include <stdio.h>
#include <string.h>
int main() {
char str1[50] = "Hello ";
char str2[] = "World";
char str3[50] = "Good ";
// Concatenate strings
strcat(str1, str2);
printf("Concatenated: %s\n", str1);
// Concatenate n characters
strncat(str3, "Morning Everyone", 7);
printf("Partial concatenation: %s\n", str3);
return 0;
}String Comparison (strcmp, strncmp)
#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("Comparing '%s' and '%s': %d\n", str1, str2, result1);
printf("Comparing '%s' and '%s': %d\n", str1, str3, result2);
if (strcmp(str1, str3) == 0) {
printf("Strings are equal\n");
}
// Compare first n characters
if (strncmp("hello", "help", 3) == 0) {
printf("First 3 characters match\n");
}
return 0;
}String Searching Functions
Character Search (strchr, strrchr)
#include <stdio.h>
#include <string.h>
int main() {
char text[] = "programming";
char ch = 'r';
// Find first occurrence
char *first = strchr(text, ch);
if (first != NULL) {
printf("First '%c' found at position: %ld\n", ch, first - text);
}
// Find last occurrence
char *last = strrchr(text, ch);
if (last != NULL) {
printf("Last '%c' found at position: %ld\n", ch, last - text);
}
return 0;
}Substring Search (strstr)
#include <stdio.h>
#include <string.h>
int main() {
char text[] = "The quick brown fox jumps";
char pattern[] = "brown";
char *found = strstr(text, pattern);
if (found != NULL) {
printf("Pattern '%s' found at position: %ld\n", pattern, found - text);
printf("Remaining text: %s\n", found);
} else {
printf("Pattern not found\n");
}
return 0;
}Practical String Applications
Word Count Program
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int countWords(char *str) {
int count = 0;
int inWord = 0;
for (int i = 0; str[i] != '\0'; i++) {
if (isspace(str[i])) {
inWord = 0;
} else if (!inWord) {
inWord = 1;
count++;
}
}
return count;
}
int main() {
char sentence[200];
printf("Enter a sentence: ");
fgets(sentence, sizeof(sentence), stdin);
printf("Word count: %d\n", countWords(sentence));
return 0;
}String Reversal
#include <stdio.h>
#include <string.h>
void reverseString(char *str) {
int len = strlen(str);
int start = 0;
int end = len - 1;
while (start < end) {
char temp = str[start];
str[start] = str[end];
str[end] = temp;
start++;
end--;
}
}
int main() {
char text[] = "Hello World";
printf("Original: %s\n", text);
reverseString(text);
printf("Reversed: %s\n", text);
return 0;
}Palindrome Check
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int isPalindrome(char *str) {
int left = 0;
int right = strlen(str) - 1;
while (left < right) {
// Skip non-alphabetic characters
while (left < right && !isalpha(str[left])) left++;
while (left < right && !isalpha(str[right])) right--;
if (tolower(str[left]) != tolower(str[right])) {
return 0;
}
left++;
right--;
}
return 1;
}
int main() {
char text[] = "A man a plan a canal Panama";
printf("Text: %s\n", text);
if (isPalindrome(text)) {
printf("It's a palindrome!\n");
} else {
printf("Not a palindrome.\n");
}
return 0;
}String Tokenization
#include <stdio.h>
#include <string.h>
int main() {
char sentence[] = "apple,banana,orange,grape";
char *token;
int count = 1;
printf("Original string: %s\n", sentence);
printf("Tokens:\n");
token = strtok(sentence, ",");
while (token != NULL) {
printf("%d. %s\n", count++, token);
token = strtok(NULL, ",");
}
return 0;
}String Conversion Functions
Case Conversion
#include <stdio.h>
#include <ctype.h>
void toUpperCase(char *str) {
for (int i = 0; str[i]; i++) {
str[i] = toupper(str[i]);
}
}
void toLowerCase(char *str) {
for (int i = 0; str[i]; i++) {
str[i] = tolower(str[i]);
}
}
int main() {
char text1[] = "Hello World";
char text2[] = "PROGRAMMING";
printf("Original: %s\n", text1);
toUpperCase(text1);
printf("Uppercase: %s\n", text1);
printf("Original: %s\n", text2);
toLowerCase(text2);
printf("Lowercase: %s\n", text2);
return 0;
}Common Mistakes and Solutions
Buffer Overflow Prevention
#include <stdio.h>
#include <string.h>
int main() {
char dest[10];
char source[] = "This is a very long string";
// Dangerous - no bounds checking
// strcpy(dest, source); // Buffer overflow!
// Safe approach
strncpy(dest, source, sizeof(dest) - 1);
dest[sizeof(dest) - 1] = '\0'; // Ensure null termination
printf("Safe copy: %s\n", dest);
return 0;
}Proper String Comparison
#include <stdio.h>
#include <string.h>
int main() {
char *str1 = "hello";
char *str2 = "hello";
char str3[] = "hello";
// Wrong way - compares addresses
if (str1 == str3) {
printf("This may not work as expected\n");
}
// Correct way - compares content
if (strcmp(str1, str3) == 0) {
printf("Strings are equal\n");
}
return 0;
}Best Practices
- Always Check Bounds: Use functions like strncpy, strncat
- Null Termination: Ensure strings are properly terminated
- Input Validation: Validate user input for security
- Use fgets: Prefer fgets over gets for input
- Memory Management: Be careful with dynamic string allocation
Summary
String handling in C requires careful attention to memory management and null termination. Key functions from string.h library provide essential operations like copying, concatenation, comparison, and searching. Understanding these fundamentals enables effective text processing, user input handling, and data manipulation in C programs. Always prioritize safety by using bounded string functions and proper input validation.
Part of BCA Programming with C Course (UGCOA22J201)