Strings are defined as an array of characters. The difference between a character array and a string is the string is terminated with a special character ‘\0’( NULL character ). String is a one dimensional array of character. We can initialize the string as char name[]={‘r’,’a’,’j’,’u’,’\0’}; Here each character occupies 1 byte of memory and last character is always NULL character.
For example:
char s[ ] = “c string”;
When the compiler encounters a sequence of characters enclosed in the double quotation marks, it appends a null character \0 at the end by default.
| c | s | t | r | i | n | g | \0 |
How to declare a string?
Here’s how you can declare strings:
char s[5];
| s0 | s1 | s2 | s3 | s4 |
How to initialize strings?
You can initialize strings in a number of ways.
char c[] = "abcd";
char c[50] = "abcd";
char c[] = {'a', 'b', 'c', 'd', '\0'};
char c[5] = {'a', 'b', 'c', 'd', '\0'};| a | b | c | d | \0 |
Let’s take another example:
char c[5] = “abcde”;
Here, we are trying to assign 6 characters (the last character is ‘\0’) to a char array having 5 characters.This is bad and you should never do this.
Example 1: scanf() to read a string
#include <stdio.h>
int main()
{
char name[20];
printf("Enter name: ");
scanf("%s", name);
printf("Your name is %s.", name);
return 0;
}Output
Enter name: Dennis Ritchie
Your name is Dennis.Even though Dennis Ritchie was entered in the above program, only “Ritchie” was stored in the name string. It’s because there was a space after Dennis.
The scanf( ) function reads the sequence of characters until it encounters whitespace (space, newline, tab etc.).
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.
Example 2: fgets() and puts()
#include <stdio.h>
int main()
{
char name[20];
printf("Enter name: ");
fgets(name, sizeof(name), stdin); // read string
printf("Name: ");
puts(name); // display string
return 0;
}Output
Enter name: Dennis Ritchie
Name: Dennis RitchieHere, we have used fgets() function to read a string from the user.
fgets(name, sizeof(name), stdlin); // read string
The sizeof(name) results to 20. Hence, we can take a maximum of 20 characters as input which is the size of the name string. To print the string, we have used puts(name);.
Note: The gets() function can also be to take input from the user. However, it is removed from the C standard. It’s because gets() allows you to input any length of characters. Hence, there might be a buffer overflow.
Example 3: Passing 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 string to a function.
return 0;
}
void displayString(char str[])
{
printf("String Output: ");
puts(str);
}Strings and Pointers
Similar like arrays, string .Hence, you can use pointers to manipulate elements of the string.
** We will discuss it after completing Pointers . So if you can skip it now.
Example 4: Strings and Pointers
#include <stdio.h>
int main( )
{
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
}String Manipulations In C Programming Using Library Functions
You need to often manipulate strings according to the need of a problem. Most, if not all, of the time string manipulation can be done manually but, this makes programming complex and large. To solve this, C supports a large number of string handling functions in the standard library “string.h”.
Few commonly used string handling functions are discussed below:
| Function | Work of Function |
| strlen( ) | computes string’s length |
| strcpy( ) | copies a string to another |
| strrev( ) | reversing a string |
| strcat( ) | concatenates(joins) two strings |
| strcmp( ) | compares two strings |
| strlwr( ) | converts string to lowercase |
| strupr( ) | converts string to uppercase |
Strings handling functions are defined under “string.h” header file.
Functions gets() and puts() are two string functions to take string input from the user and display it respectively.
#include<stdio.h>
int main()
{
char name[30];
printf("Enter name: ");
gets(name); //Function to read string from user.
printf("Name: ");
puts(name); //Function to display string.
return 0;
}Note: Though, gets() and puts() function handle strings, both these functions are defined in “stdio.h” header file.
Calculate Length of String without Using strlen() Function
#include <stdio.h>
int main()
{
char s[] = "Programming is easy";
int i;
for (i = 0; s[i] != '\0'; ++i);
printf("Length of the string: %d", i);
return 0;
}Output
Length of the string: 19Here, using a for loop, we have iterated over characters of the string from i = 0 to until ‘\0’ (null character) is encountered. In each iteration, the value of i is increased by 1. When the loop ends, the length of the string will be stored in the i variable.
Copy String Without Using strcpy()
#include <stdio.h>
int main()
{
char s1[100], s2[100], i;
printf("Enter string s1: ");
fgets(s1, sizeof(s1), stdin);
for (i = 0; s1[i] != '\0'; ++i)
{
s2[i] = s1[i];
}
s2[i] = '\0';
printf("String s2: %s", s2);
return 0;
}Output
Enter string s1: Sudipta Hazra.
String s2: Sudipta Hazra.The above program copies the content of string s1 to string s2 manually.
Concatenate Two Strings Without Using strcat()
#include <stdio.h>
int main()
{
char s1[20] = "Urmi", s2[20] = "Sarkar",s[50];
int i, j;
for (i = 0; s1[i] != '\0'; i++)
{
s[i]= s1[i];
}
s[i++] = ' ' ;
for (j = 0; s2[j] != '\0'; ++j, ++i)
{
s[i] = s2[j];
}
// terminating s string
s[i] = '\0';
printf("After concatenation: ");
puts(s);
return 0;
}Output
After concatenation: Urmi SarkarReverse a string without using strrev( )
#include <stdio.h>
#include<string.h>
void main()
{
char str[50], st;
int k = 0, l;
printf("\nEnter the string :");
gets(str);
l = strlen(str) -1;
while (k < l)
{
st = str[k];
str[k] = str[l];
str[l] = stp;
k++;
l--;
}
printf("\nReverse string is : %s", str);
getch();
}Output
Enter the string : makaut
Reverse string is : tuakamCompare two strings without using strcmp( )
#include <stdio.h>
#include <string.h>
int main()
{
char str1[20], str2[20];
int k = 0;
printf("\nEnter 1st string :");
gets(str1);
printf("\nEnter 2nd string :");
gets(str2);
while(str1[k] == str2[k] && str1[k] !='\0' || str2[k] !='\0')
{
k++;
}
if(str1[k] =='\0' && str2[k] =='\0')
printf("\nStrings are equal");
else
printf("\nStrings are unequal");
return (0);
}Output
Enter 1st string : madam
Enter 2nd string : madan
Strings are unequalCheck weather a string is palindrome or not.
#include <stdio.h>
#include <string.h>
int main()
{
char str1[20], str2[20];
int k = 0;
printf("\nEnter the string :");
gets(str1);
strcpy(str2, str1); // Copying input string
strrev(str2); // Reversing the string
if (strcmp(str1, str2) == 0) // Comparing input string with the reverse string
printf("\nThe string is a palindrome.");
else
printf("\nThe string isn't a palindrome.");
return (0);
}Output
Enter the string : madam
The string is a palindrome.