String handling using library functions - Mini Project: Build & Apply

String handling using library functions

📖 Scenario: You are working on a simple program that processes a user's name. You want to learn how to use C library functions to handle strings easily.

🎯 Goal: Build a program that stores a name, calculates its length, copies it to another string, and compares it with another name using C string library functions.

📋 What You'll Learn

Create a character array called name with the exact value "Alice".

Create an integer variable called length to store the length of name.

Create a character array called copy to hold a copy of name.

Create a character array called other with the exact value "Bob".

Use strlen to find the length of name.

Use strcpy to copy name into copy.

Use strcmp to compare name and other.

Print the length of name, the copied string, and the comparison result.

💡 Why This Matters

🌍 Real World

String handling is essential in programs that process text, like user names, messages, or file paths.

💼 Career

Many software jobs require manipulating strings safely and efficiently using standard library functions.

1

DATA SETUP: Create the initial string variable

Create a character array called name and set it to the string "Alice".

C

# Your code here

Hint

Use char name[] = "Alice"; to create the string.

2

CONFIGURATION: Add variables for length and another string

Add an integer variable called length and a character array called copy with size 10.

C

#include 
#include 

int main() {
    char name[] = "Alice";
    // Add length and copy variables below
    
    return 0;
}

Hint

Use int length; and char copy[10]; to declare the variables.

3

CORE LOGIC: Use library functions to get length and copy string

Use strlen to set length to the length of name. Use strcpy to copy name into copy. Also create a character array called other with the value "Bob" and use strcmp to compare name and other, storing the result in an integer variable called cmp.

C

#include 
#include 

int main() {
    char name[] = "Alice";
    int length;
    char copy[10];
    // Use strlen, strcpy, and strcmp below
    
    return 0;
}

Hint

Use length = strlen(name);, strcpy(copy, name);, and cmp = strcmp(name, other);.

4

OUTPUT: Print the results

Print the length of name using printf with the message Name length: . Print the copied string copy with the message Copied name: . Print the comparison result cmp with the message Comparison result: .

C

#include 
#include 

int main() {
    char name[] = "Alice";
    int length;
    char copy[10];
    length = strlen(name);
    strcpy(copy, name);
    char other[] = "Bob";
    int cmp = strcmp(name, other);
    // Print the results below
    
    return 0;
}

Hint

Use printf to show the length, copied string, and comparison result.

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