Why does this C program to calculate string's length give a wrong output?

Question

I have written this program which accepts a string as an input and return the length of it.

#include<stdio.h>
#include<string.h>
#define MAX 100

int main()
{
    char a[MAX];
    int len;
    printf("Enter a string: ");
    fgets(a, MAX, stdin);

    len = strlen(a);
    printf("Length of the string = %d", len);

    return 0;
}

Since the function strlen() doesn't count null character i.e. '\0', why is my output always 1 more than the characters of input string?

For Example -

Enter a string: Aryan
Length of the string = 6
Process returned 0 (0x0)   execution time: 4.372 s
Press any key to continue.

Answer 1

The function fgets can append to the entered string the new line character '\n' if there is a space in the supplied array.

From the C Standard (7.21.7.2 The fgets function)

2 The fgets function reads at most one less than the number of characters specified by n from the stream pointed to by stream into the array pointed to by s. No additional characters are read after a new-line character (which is retained) or after end-of-file. A null character is written immediately after the last character read into the array

Thus in this call of strlen

len = strlen(a);

the new line character is also counted.

You need to remove it as for example

a[ strcspn( a, "\n" ) ] = '\0';

or

char *p = strchr( a, '\n' );
if ( p != NULL ) *p = '\0';