C Language Strings

In this tutorial, you will learn about strings in C language programming. You will learn to declare them, initialize them, and use them in various I / O（Input/Output）operation.

In C language programming, strings are character sequences that end with a null character \0. For example:

char c[] = "c string";

When the compiler encounters a character sequence \0 enclosed in double quotes, it will default to append a null character at the end.

How to declare a string?

The method to declare a string is as follows:

char s[5];

Here, we declared a5A string of characters.

How to initialize strings?

You can initialize strings in many ways.

char c[] = "abcd";
char c[50] = "abcd";
char c[] = {'a', 'b', 'c', 'd', '\0'};
char c[5] = {'a', 'b', 'c', 'd', '\0'};

Let's take another example:

char c[5] = "abcde";

Here, we try to assign6Characters (the last character is '\0') allocated to char have5An array of characters. This is a wrong practice, you should never do this.

Assigning values to strings

Once arrays and strings are declared in C language, they do not support assignment operators.

char c[100];
c = "C programming";　　//　Error! Array type cannot be allocated.

Note:Usestrcpy() functionInstead of copying strings.

Read strings from the user

You can use the scanf() function to read strings.

scanf() function reads a character sequence until it encounters a space (space, newline, tab, etc.).

Example1：scanf() reads strings

#include <stdio.h>
int main()
{
　　　　char name[20];
　　　　printf("Input name: ");
　　　　scanf("%s",　name);
　　　　printf("Your name is　%s.",　name);
　　　　return 0;
}

Output result

Enter name:　Dennis　Ritchie
Your name is　Dennis.

Even if 'Dennis Ritchie' is entered in the above program, only 'Dennis' is in the name string. Because there is a space after Dennis.

How to read a line of text?

You can use the fgets() function to read a line of string. And you can use puts() to display the string.

Example2Fgets() and puts()

#include <stdio.h>
int main()
{
　　　　char name[30];
　　　　printf("Input name: ");
　　　　fgets(name, sizeof(name), stdin);　　//Reading a string
　　　　printf("Name: ");
　　　　puts(name);　　　　//Display string
　　　　return 0;
}

Output result

Input name: Tom Hanks
Name: Tom Hanks

Here, we have used the fgets() function to read a string from the user.

fgets(name, sizeof(name), stdlin);　//Reading a string

The result of sizeof(name) is30. Therefore, we can accept up to30 characters as input, which is the size of the name string.

To print a string, we used put (name);

Note:The gets() function can also accept user input. However, it has been removed from the C standard.
This is because gets() allows you to input characters of arbitrary length. Therefore, buffer overflow may occur.

Passing a string to a function

A string can be passed to a function in a way similar to an array. Learn more aboutPassing an array to a functionMore information.

Example3Passing a string to a function

#include <stdio.h>
void displayString(char str[]);
int main()
{
　　　　char str[50];
　　　　printf("Enter string: ");
　　　　fgets(str, sizeof(str), stdin);　　　　　　　　　　　　　
　　　　displayString(str);　　　　　//Passing a string to a function　　　
　　　　return 0;
}
void displayString(char str[])
{
　　　　printf("String output: ");
　　　　puts(str);
}

String and Pointer

Like an array, the string name "decays" to a pointer. Therefore, you can use pointers to manipulate the elements of a string. We recommend that you check the example before you proceed.C Arrays and Pointers.

Example4String and Pointer

#include <stdio.h>
int main(void) {
　　char name[] = "Harry Potter";
　　printf("%c,"}}　*name);　　　　　//　Output: H
　　printf("%c,"}}　*(name+1));　　　//　Output: a
　　printf("%c,"}}　*(name+7));　　　//　Output:　o
　　char　*namePtr;
　　namePtr = name;
　　printf("%c,"}}　*namePtr);　　　　　//　Output: H
　　printf("%c,"}}　*(namePtr+1));　　　//　Output: a
　　printf("%c,"}}　*(namePtr+7));　　　//　Output:　o
}

Common String Functions

• strlen() -Calculating the Length of a String

• strcpy() -Copying a String to Another

• strcmp() -Comparing Two Strings

• strcat() -Concatenating Two Strings