C Program to Find Length of String

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In this tutorial, you will learn and get code about how to find and print the length of any given string by user (at run-time) using following approaches:

using strlen() Function
without using strlen() Function
using user-defined Function

Print length of String using strlen() Function

To find the length of any given string in C programming, you have to ask from the user to enter the string and then find its length using strlen() function of string.h library as shown in the program given below:

#include<stdio.h>
#include<conio.h>
#include<string.h>
int main()
{
    char str[20];
    int len;
    printf("Enter the string: ");
    gets(str);
    len = strlen(str);
    printf("\nLength of the string = %d", len);
    getch();
    return 0;
}

As the above program was written under Code::Blocks IDE, therefore after successful build and run, here is the first snapshot of sample run:

Now supply any string say codescracker and press ENTER key to see the length of given string as shown here in the second snapshot:

The function named strlen() takes one argument as string and will return the length. Therefore, here the length of the string say str gets returned by the function strlen() and initialized to the variable len. Print the value of len as output.

Find Length of String without using strlen() Function

This program does not uses strlen() function to find the length, rather length gets calculated manually here:

#include<stdio.h>
#include<conio.h>
int main()
{
    char ch[20];
    int count=0, i;
    printf("Enter any string: ");
    scanf("%s", ch);
    for(i=0; ch[i]!='\0'; i++)
        count++;
    printf("\nLength of the String = %d", count);
    getch();
    return 0;
}

Here is its sample run:

c program print string length without library

Supply any string input say codescracker and press ENTER key to see its length as output:

print string length without library function c

As in above program, the string was received from the user using scanf() function. Therefore whenever user will provide any string that contains spaces, then only first word will be received and rest gets skipped. Here is the sample run where user entered any string that contains space say codes cracker:

As you can see, the word before space is codes, therefore the program will only calculate the length of codes that will be 5. To solve this problem, we have to use gets() function in place of scanf() to receive the string (along with spaces) from user as shown in the program given below:

#include<stdio.h>
#include<conio.h>
int main()
{
    char str[100];
    int count=0, i;
    printf("Enter any string: ");
    gets(str);
    for(i=0; str[i]!='\0'; i++)
        count++;
    printf("\nLength of the String = %d", count);
    getch();
    return 0;
}

Here is the final snapshot of the first sample run:

Now let's take another sample run where user enters the string that contains space say codes cracker. Here is the final snapshot of the second sample run:

Program Explained

Receive any string as input using gets() function
Use for loop to start from the first character of the string to the last
If the null terminated character ('\0') occurs, it means nothing left inside the string
Therefore, until the null terminated character comes, increase the value of count variable each and every time the program flow goes inside the for loop
The count variable is initialized to 0 at beginning of the program
Therefore, from first character to the last character of the string, the count variable will be incremented each and every time
It means, count variable at last, will holds the length of the string, that is how many character present inside the string say str
Finally print the value of count that shows the length of the string

Find String Length using User-defined Function

This program is made using user-defined function to do the same job as of previous one:

#include<stdio.h>
#include<conio.h>
int findStringLen(char str[50]);
int main()
{
    char str[50];
    int len;
    printf("Enter any string: ");
    gets(str);
    len = findStringLen(str);
    printf("\nLength of the String = %d", len);
    getch();
    return 0;
}
int findStringLen(char s[50])
{
    int i, count=0;
    for(i=0; s[i]!='\0'; i++)
        count++;
    return count;
}

Here is the final snapshot of the sample run:

Same Program in Other Languages

C Online Test

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