To understand this example, you should have the knowledge of the following C programming topics:
·      
Relationship Between Arrays and Pointers
·      
C Pass Addresses and Pointers
As you know, the best way to find the length of a string is
by using the strlen() function. However, in this example, we will
find the length of a string manually.
Calculate Length of String without Using strlen() Function
#include <stdio.h>
int main() {
    char s[] = "Programming is fun";
    int i;
    for (i = 0; s[i] != '\0'; ++i);
    
    printf("Length of the string: %d", i);
    return 0;
}
Output
Length of the string: 18
Here, using
a for loop, we have iterated over characters of
the string from i = 0 to until '\0' (null
character) is encountered. In each iteration, the value of i is increased by 1.
When
the loop ends, the length of the string will be stored in the i variable.
Note: Here,
the array s[] has
19 elements. The last element s[18] is the null character '\0'. But our loop does not count this character as
it terminates upon encountering it.