The Program in C to Calculate length of a string using pointer is given below:

#include <stdio.h>

int string_length(char *str) {
    int count = -1;
    while (*str != '\0') {
        count++;
        str++;
    }
    return count;
}

int main() {
    char str[100];
    printf("Enter a string: ");
    fgets(str, 100, stdin);

    int length = string_length(str);
    printf("The length of the string is: %d\n", length);

    return 0;
}

Output:

Enter a string: i am cool as wind
The length of the string is: 17

Pro-Tips💡

In the string_length function, the pointer str is passed as an argument.

The function uses the pointer to iterate through the string until the null character ‘\0’ is found.

The function increments a counter variable for each character that it encounters, and once it reaches the null character, it returns the count as the length of the string.

The pointer str is used to access each character of the string by incrementing it in each iteration of the loop, which is a way of accessing the memory address of the next character in the string.

In the main function, the fgets function reads the string input from the user and stores it in the variable str, which is a char array and also a pointer to the first element of the array.

This pointer is then passed to the string_length function as an argument, where it is used to access the string and calculate its length.