String handling using library functions - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to copy the string from source to destination using a standard library function.

C

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

int main() {
    char source[] = "Hello";
    char destination[10];
    [1](destination, source);
    printf("%s", destination);
    return 0;
}

Drag options to blanks, or click blank then click option'

Astrcpy

Bstrlen

Cstrcmp

Dstrcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using strcmp instead of strcpy, which compares strings but does not copy.

Using strlen which returns length, not copying.

Using strcat which concatenates strings instead of copying.

The strcpy function copies the string from the source to the destination.

2fill in blank

medium

Complete the code to find the length of the string using a standard library function.

C

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

int main() {
    char str[] = "Hello, world!";
    int length = [1](str);
    printf("Length: %d", length);
    return 0;
}

Drag options to blanks, or click blank then click option'

Astrlen

Bstrcpy

Cstrcmp

Dstrcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using strcpy which copies strings, not length.

Using strcmp which compares strings, not length.

Using strcat which concatenates strings, not length.

The strlen function returns the length of the string excluding the null character.

3fill in blank

hard

Fix the error in the code to compare two strings correctly using a standard library function.

C

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

int main() {
    char str1[] = "apple";
    char str2[] = "apple";
    if ([1](str1, str2) == 0) {
        printf("Strings are equal\n");
    } else {
        printf("Strings are different\n");
    }
    return 0;
}

Drag options to blanks, or click blank then click option'

Astrcpy

Bstrcmp

Cstrlen

Dstrcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using strcpy which copies strings, not compares.

Using strlen which returns length, not compares.

Using strcat which concatenates strings, not compares.

The strcmp function compares two strings and returns 0 if they are equal.

4fill in blank

hard

Fill both blanks to concatenate two strings safely using a standard library function.

C

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

int main() {
    char str1[20] = "Hello, ";
    char str2[] = "World!";
    [1](str1, str2, [2]);
    printf("%s", str1);
    return 0;
}

Drag options to blanks, or click blank then click option'

Astrncat

Bstrcpy

Csizeof(str1) - strlen(str1) - 1

Dstrlen(str2)

Attempts:

3 left

💡 Hint

Common Mistakes

Using strcpy which overwrites instead of appending.

Using strlen(str2) which may cause overflow if str1 is small.

Not calculating buffer size correctly.

The strncat function concatenates strings safely by specifying the maximum number of characters to append. The size calculation ensures no buffer overflow.

5fill in blank

hard

Fill all three blanks to create a substring by copying part of a string using standard library functions.

C

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

int main() {
    char source[] = "Programming";
    char substring[10];
    strncpy(substring, source + [1], [2]);
    substring[[3]] = '\0';
    printf("%s", substring);
    return 0;
}

Drag options to blanks, or click blank then click option'

A3

B6

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Not adding the null terminator, causing garbage output.

Copying wrong number of characters.

Starting from wrong index.

The code copies 6 characters starting from index 3 of the source string. Then it adds a null character at index 6 to end the substring properly.

Practice

1. Which library function in C is used to find the length of a string (excluding the null character)?

easy

A. strcpy()

B. strcat()

C. strcmp()

D. strlen()

Solution

1. Step 1: Understand the purpose of strlen()

   The function strlen() counts characters in a string until it reaches the null terminator '\0', giving the string length.

2. Step 2: Compare with other functions

   strcpy() copies strings, strcmp() compares strings, strcat() concatenates strings, so they do not measure length.

3. Final Answer:

   strlen() -> Option D

4. Quick Check:

   Length function = strlen() [OK]

Hint: Length means count chars before '\0', use strlen() [OK]

Common Mistakes:

• Confusing strcpy() with strlen()
• Using strcmp() to get length
• Forgetting null terminator in length count

2. Which of the following is the correct syntax to copy string src into dest using a standard library function?

easy

A. strcpy(src, dest);

B. strcpy(dest, src);

C. strcpy(dest);

D. strcpy(src);

Solution

1. Step 1: Recall strcpy() function signature

   strcpy() takes two arguments: destination string first, then source string to copy from.

2. Step 2: Check each option

   Only strcpy(dest, src); matches the correct order and argument count.

3. Final Answer:

   strcpy(dest, src); -> Option B

4. Quick Check:

   Copy syntax = strcpy(dest, src) [OK]

Hint: Destination first, source second in strcpy() [OK]

Common Mistakes:

• Swapping source and destination arguments
• Using only one argument
• Missing semicolon or parentheses

3. What will be the output of the following C code?

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

int main() {
    char str1[20] = "Hello";
    char str2[] = "World";
    strcat(str1, str2);
    printf("%s", str1);
    return 0;
}

medium

A. HelloWorld

B. Hello World

C. WorldHello

D. Hello

Solution

1. Step 1: Understand strcat() behavior

   strcat() appends the second string to the end of the first string without adding spaces.

2. Step 2: Analyze the code output

   str1 starts as "Hello", str2 is "World". After strcat(str1, str2), str1 becomes "HelloWorld".

3. Final Answer:

   HelloWorld -> Option A

4. Quick Check:

   Concatenate without space = HelloWorld [OK]

Hint: strcat joins strings directly, no spaces added [OK]

Common Mistakes:

• Expecting a space between strings
• Confusing strcat() with strcpy()
• Not allocating enough space in destination

4. Identify the error in the following code snippet:

#include <string.h>

int main() {
    char s1[5] = "Data";
    char s2[] = "Science";
    strcat(s1, s2);
    return 0;
}

medium

A. Missing #include <stdio.h>

B. strcat() syntax is incorrect

C. s1 array size is too small for concatenation

D. s2 should be declared as char *s2

Solution

1. Step 1: Check array sizes for strcat()

   s1 has size 5, holding "Data" plus '\0'. Concatenating "Science" (7 chars) will overflow s1.

2. Step 2: Verify other options

   strcat() syntax is correct, #include <stdio.h> is not mandatory here, and s2 declaration is valid as array.

3. Final Answer:

   s1 array size is too small for concatenation -> Option C

4. Quick Check:

   Buffer overflow risk = s1 too small [OK]

Hint: Destination array must fit combined strings [OK]

Common Mistakes:

• Ignoring buffer size for strcat()
• Assuming strcat() adds space automatically
• Confusing array and pointer declarations

5. Given two strings char s1[] = "apple"; and char s2[] = "apricot";, which library function call correctly checks if s1 comes before s2 in dictionary order?

hard

A. strcmp(s1, s2) < 0

B. strcmp(s1, s2) > 0

C. strcmp(s2, s1) < 0

D. strcmp(s2, s1) > 0

Solution

1. Step 1: Understand strcmp() return values

   strcmp() returns a negative value if first string is lexicographically less than second, zero if equal, positive if greater.

2. Step 2: Apply to given strings

   "apple" comes before "apricot", so strcmp(s1, s2) returns negative, meaning strcmp(s1, s2) < 0 is true.

3. Final Answer:

   strcmp(s1, s2) < 0 -> Option A

4. Quick Check:

   Lex order check = strcmp(s1, s2) < 0 [OK]

Hint: strcmp() negative means first string is before second [OK]

Common Mistakes:

• Reversing argument order in strcmp()
• Checking for > 0 instead of < 0
• Assuming strcmp() returns boolean