Count the length of a string in C

str_len.c

#include <stdio.h>
#include <stdlib.h>

int calc_len_str(const char *str);

int main()
{
    char str[] = "How are you today!";
    int result = calc_len_str(str);
    printf("result 1 = %d\n", result);
    if (result != 18)
        return 1;
    int result2 = calc_len_str2(str);
    if (result2 != 18)
        return 1;
    printf("result 2 = %d\n", result2);
    return 0;
}

int calc_len_str(const char *str)
{
    int count = 0;
    while(*str)
    {
        *str++;
        count++;
    }

    return count;
}

int calc_len_str2(const char *str)
{
    const char *lastAddr = str;
    while(*lastAddr)
        *lastAddr++;
    return lastAddr - str;
}