📃 C String Functions Explained with Examples

⬅️ Previous

🧵 String Operations and Functions in C

🔹 What is a String in C?

In C, a string is a sequence of characters terminated by a null character '\0'.

char name[10] = "Arif";

Here, name contains: {'A', 'r', 'i', 'f', '\0'}

🔹 Declaring Strings

char str1[] = "Hello";        
char str2[6] = {'H','e','l','l','o','\0'};

🔹 Input and Output of Strings

#include <stdio.h>

int main() {
    char name[50];
    printf("Enter your name: ");
    scanf("%s", name); 
    printf("Hello, %s\n", name);
    return 0;
}

📌 Note: Use fgets() instead of scanf() if input has spaces:

fgets(name, sizeof(name), stdin);

🧰 Common String Functions in C

Add this header:

#include <string.h>

✅ 1. strlen() – String Length

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

int main() {
    char str[] = "OpenAI";
    printf("Length = %lu\n", strlen(str));
    return 0;
}

✅ 2. strcpy() – Copy One String to Another

char src[] = "Hello";
char dest[20];
strcpy(dest, src);

✅ 3. strcat() – Concatenate Strings

char a[50] = "Hello ";
char b[] = "World";
strcat(a, b);

✅ 4. strcmp() – Compare Strings

int result = strcmp("abc", "abc");   // 0
int result2 = strcmp("abc", "abd");  // negative

✅ 5. strchr() – Find Character in String

char *ptr = strchr("Bangladesh", 'g');

✅ 6. strstr() – Find Substring

char *sub = strstr("Programming", "gram");

❌ Bonus: strrev() – Reverse String (Non-standard)

char str[] = "OpenAI";
strrev(str);

🎯 Full Example Program

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

int main() {
    char str1[100] = "Hello";
    char str2[100] = "World";
    
    printf("str1: %s\n", str1);
    printf("str2: %s\n", str2);

    printf("Length of str1: %lu\n", strlen(str1));

    strcpy(str2, str1);
    printf("After strcpy, str2: %s\n", str2);

    strcat(str1, " C");
    printf("After strcat, str1: %s\n", str1);

    if (strcmp(str1, str2) == 0)
        printf("str1 and str2 are equal.\n");
    else
        printf("str1 and str2 are different.\n");

    return 0;
}

🧠 Summary Table

FunctionPurpose
strlen()Get string length
strcpy()Copy one string to another
strcat()Append strings
strcmp()Compare two strings
strchr()Locate character in string
strstr()Find substring

💡 Tips for Working with Strings

  • Always ensure enough memory space.
  • Include <string.h> for built-in functions.
  • Avoid buffer overflows.
  • Prefer fgets() over gets() for safer input.
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C String Functions Explained with Examples

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