C Program to Find Length of a String

How to write a C program to find string length using strlen and without using the function. We can calculate the string length either by using the Inbuilt C function or without using the strlen library function.

C strlen Function

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

strlen(<string name>)

The C 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 using strlen function

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

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

Within this C strlen function example program, We declared a character array variable of size 100 and named it Str, and we also declared one integer variable, Length.

The below printf statements ask the user to enter any word they want to find the length.

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

The below statement in this program will assign the user entered string to the Str variable.

gets (Str);

In the next line, we have strlen,

lg = strlen(Str);

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

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

printf(" Length = %d \n", lg);

From the above screenshot, you can observe that we entered the 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 the same in multiple ways, 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 character array, and it will find the length of a string without using a C 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;
}

If you look at the While loop in this program for string length,

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

Every string ends with the null character “\0”. So, the condition inside the while loop (Str[Length] != ‘\0’) will fail when the string reaches the “\0” position.

Inside the while loop, we are using the Increment Operator to increase the value of Length by 1.

Within this example, we haven’t used c strlen. The 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, the length incremented to 1

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

Third Iteration: The Value of Length is 2
(Str[2] != ‘\0’) condition is TRUE because Str[2] = u. So, the length incremented by 1

Fourth Iteration: Length = 3, the While condition (Str[3] != ‘\0’) is FALSE because Str[3] = \0. So, the loop in this C strlen example will terminate.

The 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 of the Length of s String = 3

C Program to Find Length of a String Using For Loop

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

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

We haven’t done anything special in this example. We just changed the while loop in the above code to a for loop. Suppose you have any queries regarding the for loop. Please refer to the For Loop article here: For Loop.