C++ Program to Find Length of String

In this article, you will learn and get to find and print the length of any given string by user at run-time, in C++ language. The program is created with the help of these approaches:

• Find length of string without using any library or built-in function like strlen()
• using strlen() function
• using Pointer

Find Length of String without strlen() Function

To find length of a string in C++ programming, you have to ask from user to enter the string first. And then find its length as shown in the program given below.

This program finds length of a string using user-based code. That is, this program does not use library function or built-in function, strlen().

#include<iostream>
#include<stdio.h>
using namespace std;
int main()
{
    char str[200];
    int len=0, i=0;
    cout<<"Enter the String: ";
    gets(str);
    while(str[i])
    {
        len++;
        i++;
    }
    cout<<"\nLength = "<<len;
    cout<<endl;
    return 0;
}

This program was build and run under Code::Blocks IDE. Here is its sample run:

Now enter any string say codes cracker dot com and press ENTER key to find and print length of given string as shown here in the following output:

Here is another sample run with user input, codescracker:

The dry run of above program with user input, codescracker goes like:

• Initial values, len=0, i=0
• When user enters the string say codescracker as input, then it gets stored to str[] in this way:
  • str[0]=c
  • str[1]=o
  • str[2]=d
  • and so on upto
  • str[11]=r
• Now the condition of while loop gets evaluated. That is the condition, str[i] or str[0] or c evaluates to be true. Therefore program flow goes inside the loop
• When there is no any character left, then the condition evaluates to be false. That is, its condition evaluates to be false at 12^th index
• Now inside the loop, the value of len and i gets incremented. So i=1 and len=1
• Program flow goes back and evaluates the condition again. Because the condition str[i] or str[1] again evaluates to be true, therefore program flow again goes inside the loop.
• This process continues until the last character of codescracker.
• And every time the value of len gets incremented
• So when the condition of while loop evaluates to be false, then we'll have a variable, len that holds the length of string, or how many characters are available in the entered string by user at run-time
• So print the value of len as output that shows the length of given string

Find Length of String using strlen() Function

Here is another C++ program that also finds and prints length of string entered by user. The only difference with previous program is, this program uses a built-in or library function of C++ named strlen().

The function, strlen() takes string as its argument and returns its length. This function is defined in string.h header file.

#include<iostream>
#include<stdio.h>
#include<string.h>
using namespace std;
int main()
{
    char str[200];
    int len=0;
    cout<<"Enter the String: ";
    gets(str);
    len = strlen(str);
    cout<<"\nLength = "<<len;
    cout<<endl;
    return 0;
}

The output produced by this program is similar to previous program.

Find Length of String using Pointer

Now let's create the same purpose program, that is to find length of a string, but using pointer. The address of first character of string gets initialized to pointer type variable say ptr and using this variable, the length of string gets calculated.

Note - The & is called as address of operator. Whereas as the * is called as value at operator. The ptr++ (char pointer type variable) moves to next character's address

#include<iostream>
#include<stdio.h>
using namespace std;
int main()
{
    char str[200], *ptr;
    int len=0;
    cout<<"Enter the String: ";
    gets(str);
    ptr = &str[0];
    while(*ptr)
    {
        len++;
        ptr++;
    }
    cout<<"\nLength = "<<len;
    cout<<endl;
    return 0;
}

Same Program in Other Languages

• C Find Length of String
• Java Find length of String
• Python Find length of String

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