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C Program to Find Length of a String

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We can calculate the string length in C Programming in multiple way:

  1. Inbuilt string function strlen
  2. Without using library function strlen

In this article, We will show you, How to find string length using strlen and without using strlen function

strlen Function

strlen function is a built in string function in C Programming and it is used to find the string length. Syntax of the strlen function is:

strlen(<string name>)

strlen function will count the number of characters in a string until it reaches the null value (\0) and returns that integer value as output.

C Program to Find the Length of a String

This program allows the user to enter any string or character array and it will find the length of a string using built-in string function called strlen.

#include <stdio.h>
#include <string.h>
 
int main()
{
  char Str[100];
  int Length;
 
  printf("\n Please Enter any String \n");
  gets (Str);
 
  Length = strlen(Str);
 
  printf("Length of a String = %d\n", Length);
 
  return 0;
}

OUTPUT

Length of a String Using Strlen

ANALYSIS

We declared character array variable of size 100 and names as Str and we also declared 1 integer variable Length.

Below printf statements asks the user to enter any word that they would like to find the length.

printf("\n Please Enter any String \n");

Below statement will assign the user entered string to Str variable.

gets (Str);

In the next line we have,

Length = strlen(Str);

We are finding the length of a string using the strlen() function and also assigning the value to Length variable.

Below printf statement will print the value inside the Length (means string length)

printf(" Length of Your String = %d \n", Length);

From the above screenshot you can observe that, We entered string “Tutorial Gateway” and the Length of a string = 16 (including the black space in between 2 words)

C Program to Find Length of a String Without Using strlen

We can achieve this in multiple way but we will discuss two approaches called For Loop and While Loop

C Program to Find Length of a String Using While Loop

This program allows the user to enter any string or character array and it will find length of a string without using strlen function.

#include <stdio.h>
#include <string.h>
 
int main()
{
  char Str[100];
  int Length = 0;
 
  printf("\n Please Enter any String \n");
  gets(Str);
 
  while (Str[Length] != '\0')
   {   
     Length++;
   }
   
  printf("\nLength of a String = %d", Length);
  return 0;
}

OUTPUT

Length of a String Without Using strlen

ANALYSIS
If you look at the While loop,

while (Str[Length] != '\0')
 {   

     Length++;

 }

Every string ends with null character “\0”. So the condition inside the while loop (Str[Length] != ‘\0’) will fail when the string reaches “\0” position.
Inside the while loop we are using the Increment Operator to increase the value of Length by 1.

User Entered the String “you”
Initially the length value will be 0.

First Iteration
Initially the length value will be 0.
(Str[0] != ‘\0’) condition is TRUE because Str[0] = y
So length is incremented to 1

Second Iteration
Now the Value of Length is 1
(Str[1] != ‘\0’) condition is TRUE because Str[1] = o
So length is incremented to 1

Third Iteration
Now the Value of Length is 2
(Str[2] != ‘\0’) condition is TRUE because Str[2] = u
So length is incremented to 1

Fourth Iteration
Now the Value of Length becomes 3.
While condition (Str[3] != ‘\0’) is FALSE because Str[3] = \0
So the loop will be terminated.

Final printf statement will print the value inside the Length variable (means length of a string)

printf("\n Length of the String is : %d", Length);

Final output is
Length of s String = 3

C Program to Find Length of a String Using For Loop

This program allows the user to enter any string or character array and it will find length of a string without using strlen function.

#include <stdio.h>
#include <string.h>
 
int main()
{
  char Str[100];
  int i, Sum = 1;
 
  printf("\n Please Enter any String \n");
  gets(Str);
 
  for (i = 0; Str[i]!='\0'; i++);
  
  printf("Length of Your String = %d\n", i);
  return 0;
}

OUTPUT

Length of a String Using For Loop

We haven’t done anything special here, We just changed the while loop code to for loop. If you have any queries regards to for loop. Please refer For Loop article here: For Loop

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