Option A is the correct function to find the length of given string. Example: #include<stdio.h> int xstrlen(char *s) { int length=0; while(*s!='\0') { length++; s++; } return (length); } int main() { char d[] = "IndiaBIX"; printf("Length = %d\n", xstrlen(d)); return 0; } Output: Length = 8