Common string operations - Mini Project: Build & Apply

Common string operations

📖 Scenario: You are working on a simple program that processes a user's name. You want to practice basic string operations like creating a string, finding its length, copying it, and comparing it.

🎯 Goal: Build a C program that creates a string with a name, finds its length, copies it to another string, compares the two strings, and prints the results.

📋 What You'll Learn

Create a string variable with a specific name

Create an integer variable to store the string length

Use strlen to find the length of the string

Use strcpy to copy the string to another variable

Use strcmp to compare the two strings

Print the length and comparison result

💡 Why This Matters

🌍 Real World

String operations like copying, comparing, and measuring length are common in programs that handle text input, such as user names, messages, or file names.

💼 Career

Understanding basic string functions is essential for programming in C, especially in system programming, embedded systems, and software development where manual string handling is common.

1

Create the initial string

Create a character array called name and initialize it with the string "Alice".

C

# Create a character array called name and initialize it with "Alice"
// Your code here

Hint

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

2

Find the length of the string

Create an integer variable called length and set it to the length of name using strlen(name).

C

#include 
#include 

char name[] = "Alice";

// Create an integer variable length and set it to strlen(name)
// Your code here

Hint

Use int length = strlen(name); to get the string length.

3

Copy the string to another variable

Create a character array called copy with size 10. Use strcpy(copy, name) to copy the string from name to copy.

C

#include 
#include 

char name[] = "Alice";
int length = strlen(name);

// Create a char array copy with size 10 and copy name into it
// Your code here

Hint

Declare char copy[10]; and then use strcpy(copy, name);.

4

Compare the strings and print results

Create an integer variable cmp and set it to strcmp(name, copy). Then print the length and comparison result using printf with the format: Name length: %d\nComparison result: %d\n.

C

#include 
#include 

char name[] = "Alice";
int length = strlen(name);
char copy[10];
strcpy(copy, name);

// Create int cmp = strcmp(name, copy) and print length and cmp
// Your code here

Hint

Use int cmp = strcmp(name, copy); and then printf to show the results.

Practice

1. Which C function is used to find the length of a string?

easy

A. strlen

B. strcpy

C. strcmp

D. strcat

Solution

1. Step 1: Understand string length concept

   The length of a string is the number of characters before the null terminator.

2. Step 2: Identify the correct function

   strlen returns the length of a string, while strcpy copies, strcmp compares, and strcat concatenates strings.

3. Final Answer:

   strlen -> Option A

4. Quick Check:

   Length function = strlen [OK]

Hint: Remember: length = strlen, copy = strcpy [OK]

Common Mistakes:

• Confusing strcpy with strlen
• Using strcmp to get length
• Thinking strcat returns length

2. Which of the following is the correct syntax to copy string src into dest in C?

easy

A. strcat(dest, src);

B. strcpy(src, dest);

C. strlen(dest, src);

D. strcpy(dest, src);

Solution

1. Step 1: Understand strcpy parameters

   strcpy copies the source string into the destination string. The first argument is destination, second is source.

2. Step 2: Check each option

   strcpy(dest, src); uses correct order (destination first, source second). strcpy(src, dest); reverses parameters. strcat(dest, src); concatenates strings. strlen(dest, src); returns length, not copies.

3. Final Answer:

   strcpy(dest, src); -> Option D

4. Quick Check:

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

Hint: Copy: destination first, source second in strcpy [OK]

Common Mistakes:

• Swapping source and destination arguments
• Using strcat instead of strcpy for copying
• Using strlen for copying strings

3. What is the output of this C code?

char str1[20] = "Hello, ";
char str2[] = "World!";
strcat(str1, str2);
printf("%s", str1);

medium

A. Hello,

B. World!Hello,

C. Hello, World!

D. Compilation error

Solution

1. Step 1: Understand strcat behavior

   strcat appends the second string to the end of the first string.

2. Step 2: Apply strcat to given strings

   Appending "World!" to "Hello, " results in "Hello, World!" stored in str1.

3. Final Answer:

   Hello, World! -> Option C

4. Quick Check:

   Concatenate str1 + str2 = Hello, World! [OK]

Hint: strcat adds second string to end of first [OK]

Common Mistakes:

• Expecting strcat to replace string
• Confusing order of concatenation
• Assuming strcat returns new string

4. Identify the error in this code snippet:

char s1[5] = "Hello";
char s2[10];
strcpy(s2, s1);
printf("%s", s2);

medium

A. s2 array size is too small for copy

B. s1 array size is too small for "Hello"

C. strcpy parameters are reversed

D. Missing null terminator in s2

Solution

1. Step 1: Check array size for s1

   String "Hello" has 5 characters plus 1 for '\0' terminator, so s1 needs size at least 6.

2. Step 2: Analyze s1 declaration

   s1 is declared with size 5, which is too small to hold "Hello" plus null terminator, causing overflow.

3. Final Answer:

   s1 array size is too small for "Hello" -> Option B

4. Quick Check:

   String size must include '\0' [OK]

Hint: String size must fit characters + '\0' terminator [OK]

Common Mistakes:

• Ignoring null terminator size
• Assuming strcpy reverses parameters
• Thinking s2 size is too small here

5. Given the code below, what will be printed?

char text[] = "Programming in C";
char *ptr = strstr(text, "in");
printf("%s", ptr);

hard

A. in C

B. Programming in C

C. in

D. NULL

Solution

1. Step 1: Understand strstr function

   strstr returns pointer to first occurrence of substring or NULL if not found.

2. Step 2: Find substring "in" in text

   "in" first appears inside "Programming in C" starting at "in C" substring.

3. Step 3: Print from pointer

   Printing from pointer prints "in C" including the substring and rest of string.

4. Final Answer:

   in C -> Option A

5. Quick Check:

   strstr returns substring start pointer [OK]

Hint: strstr returns pointer to substring start [OK]

Common Mistakes:

• Expecting strstr to return only substring
• Confusing strstr with strcmp
• Assuming strstr returns NULL if substring found