Strings in C with Examples: String Functions

Strings in C

Strings in C are used to store and work with text, represented as arrays of characters ending with a null character (\0). This article simplifies strings in C by explaining their structure, basic operations, and important functions for easy understanding.

In this C tutorial, we'll explore what strings are, how they work, and what you need to know when working with them in the C language. To get a little deeper, consider our C Programming Course.

What are Strings in C?

A string is a sequence of characters. e.g. "ScholarHat". Many programming languages like Java have a data type known as a string for storing string values. In C, a string is stored as an array of characters. You have to use char data type and create an array of characters for a string. The string is terminated with a null character '\0'.

• Strings in C are arrays of characters ending with a null character (\0).
• Always ensure the array size is sufficient to include the null terminator.
• Use C functions like strlen(), strcpy(), strcat(), and strcmp() for string operations.
• String literals (e.g., "Hello") are read-only and cannot be modified.
• Use scanf() for input without spaces and fgets() for input with spaces.

Strings in C are represented using double quotes ("") or single quotes (''). Whenever an array of characters e.g. c[10] gets created, the compiler implicitly appends '\0' at the end of the string.

How to declare Strings in C

In C, declaration means telling the compiler about a variable or function by specifying its type and name so the program knows how to use it.For declaring Strings in C,we use the following method that are

1. Declaring a String as a Character Array

A string can be declared as an array of characters with a fixed size.

Syntax

char str[size]

This reserves space for 20 characters (including the null terminator).

2. Declaring a String Using String Literal

A string can be directly initialized using a string literal, which automatically adds the null terminator.

char str[] = "Hello"; 

This creates a string with a size equal to the number of characters in "Hello" plus the null terminator.

Initializing Strings in C

Initialization in C is the process of assigning a value to a variable at the time of its declaration. This ensures that the variable starts with a known value when it is created.

1. Using a String Literal without Specifying Size

When you initialize a string with a literal, C automatically determines the size based on the number of characters in the string, including the null terminator (\0).

Example

char str[] = "Hello"; // Size is automatically determined 

2. Using a String Literal with a Defined Size

You can specify the size of the string array in advance. If the literal is shorter than the array size, the remaining positions are filled with the null character (\0).

Example

char str[20] = "Hello";  // String is assigned with size 20 

3. Assigning Characters One by One with a Defined Size

In this method, each character is manually assigned to the array, and you explicitly define the array’s size to hold the characters, including the null terminator.

Example

 char str[6] = {'H', 'e', 'l', 'l', 'o', '\0'};  // Each character is assigned individually 

4. Assigning Characters One by One without Defining the Size

Similar to the previous method, but the size of the array is automatically set based on the number of characters you assign, including the null terminator.

Example

char str[] = {'H', 'e', 'l', 'l', 'o', '\0'};  // Size is automatically determined

Strings in C Example

Let's understand this by a given example.

#include <stdio.h>
int main(){ 
 char str1[10]={'S', 'c', 'h', 'o', 'l', 'a', 'r', 'H', 'a', 't', '\0'}; 
 char str2[10]="ScholarHat"; 
 
 printf("String by char array method: %s\n", str1); 
 printf("String by String Literal method: %s\n", str2); 
 return 0; 
} 

Here, we are printing the string, "Scholarhat" using both the methods discussed above

Note: %s is the format specifier to print a string in C.

Output

String by char array method: ScholarHat
String by String Literal method: ScholarHat

Read More - Top 50 Mostly Asked C Interview Questions

How to access a String in C?

As the string isarray of characters, we can access the characters of the string with their index number. The string index starts with 0.

Example

#include <stdio.h>
int main() {
 char str[10]="ScholarHat";
 printf("%c", str[5]);
 return 0;
}

Output

a

%c is a format specifier to print a single character.

How to modify a String in C?

To change any specific character in a string, refer to the index number the same as an array. Here you also need to use single quotes,''.

Example

#include <stdio.h>
int main() {
 char str[10]="ScholarHat";
 str[4] = 'i';
 printf("%s", str);
 return 0;
}

Output

SchoiarHat

How to loop through a string in C?

To loop through a string, for loop is used.

Example

#include <stdio.h>
int main() {
 char str[10]="ScholarHat";
 
 for (int i = 0; i < 10; ++i) {
 printf("%c\n", str[i]);
 }
 return 0;
}

Output

S
c
h
o
l
a
r
H
a
t

String Functions in C

In C programming language, several string functions canbe used to manipulate strings. To use them, you must include the <string.h> header file in your program. Here are some of the commonly used string functions in C:

Example to demonstrate some basic string functions in C Online Compiler

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

int main() {
 // Declaration and Initialization
 char str1[] = "ScholarHat";
 char str2[20];
 char search = 'o';

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

 // strcpy - String Copy
 strcpy(str2, str1);
 printf("After copying, str2: %s\n", str2);

 // strcat - String Concatenation
 strcat(str2, " welcomes");
 printf("After concatenation, str2: %s\n", str2);

 // strcmp - String Comparison
 int result = strcmp(str1, str2);
 if (result == 0) {
 printf("str1 is equal to str2\n");
 } else if (result < 0) {
 printf("str1 is less than str2\n");
 } else {
 printf("str1 is greater than str2\n");
 }

 // strchr
 char *found = strchr(str1, search);
 // Check if the character is found
 if (found != NULL) {
 printf("'%c' found at position: %ld\n", search, found - str1 + 1);
 } else {
 printf("'%c' not found in the string.\n", search);
 }

 return 0;
}

Output

Length of str1: 10
After copying, str2: ScholarHat
After concatenation, str2: ScholarHat welcomes
str1 is less than str2
'o' found at position: 4

Summary

Strings in C can be quite challenging for some, but with a little understanding of their components, anyone can quickly become proficient. From learning the basics of fundamental string operations such as concatenation, there’s much to explore and understand. If you want to become proficient in the concepts of C programming, consider joining our C Certification course.

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Take this MCQ and see how ready you are for technical interviews!

Q 1: What is the correct syntax to declare a string in C?

• (a) char str[] = "Hello";
• (b) string str = "Hello";
• (c) str = "Hello";
• (d) char str = "Hello";

Q 2: Which function is used to concatenate two strings in C?

• (a) strcat()
• (b) strjoin()
• (c) stradd()
• (d) strcatf()

Q 3: What will be the output of the following code?

#include <stdio.h>
#include <string.h>
int main() {
    char str1[] = "Hello";
    char str2[] = "Hello";
    if (strcmp(str1, str2) == 0)
        printf("Equal");
    else
        printf("Not Equal");
    return 0;
}

• (a) Equal
• (b) Not Equal
• (c) Compilation Error
• (d) Runtime Error

Q 4: How is a null character represented in C?

• (a) \n
• (b) \t
• (c) \0
• (d) NULL

Q 5: Which function is used to find the length of a string in C?

• (a) strlen()
• (b) strlength()
• (c) size()
• (d) len()