Alphabetical comparison of two strings in C -

my programming experience extremely scattered , can't seem find answer hope simple question. had assignment last week didn't finish , it's bugging me death.

i supposed compare 2 strings alphabetically without using strcmp , find out string alphabetically first via function using pointers.

int strcmp373(char *str1, char *str2) {   while(*str1 != '\0')   {     str1++;   }   while(*str2 != '\0')   {     str2++;   } if(*str1 == *str2)  } 

this horrible attempt, thought process being use null terminated value. hoping insight , explain how works?

here's copy of assignment specifications reference.

write function called strcmp373, compares 2 strings in precisely same way strcmp in c library . time, please use "pointer syntax" in writing function. is, [ ] operator should not used @ when referring particular characters in string1 , string2; instead, parameters , local variables should declared pointers (using * symbol). please sure emulate strcmp c function. note strcmp returns 0 if 2 strings equal, though 0 means false in c. sign of other return values matters used indicate in way strings not same, precise return value not important. may not use of built-in c string library functions complete code.

here prototype of function:

int strcmp373(char *, char *); 

and here main function can use test strcmp373.

#include <stdio.h> #include "hw3.h" // discussed  int main() { char str1[81], str2[81]; char again = 'y', newline; while (again == 'y') {     printf("enter string\n");     scanf("%s", str1);     printf("enter string\n");     scanf("%s", str2);     int comp = strcmp373(str1, str2);     if (comp < 0)         printf("%s alphabetically before %s\n", str1, str2);     else if (comp > 0)         printf("%s alphabetically after %s\n", str1, str2);     else printf("%s , %s same\n", str1, str2);     printf("again? (y/n)\n");     scanf("%c%c", &newline, &again); } } 

let's str1 points holds "abcd" , str2 points holds "abc".

str1 | v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+  str2 | v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+ 

when execute

while(*str1 != '\0') {   str1++; } 

you move str1 until points null character.

str1 | v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+      str1     |     v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+          str1         |         v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+              str1             |             v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+                  str1                 |                 v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+ 

similarly, when execute

while(*str2 != '\0') {   str2++; } 

you move str2 until points null character.

str2 | v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+      str2     |     v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+          str2         |         v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+              str2             |             v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+ 

when while loops done, both str1 , str2 point null character. hence, *str1 == *str2 evaluates true.

what need compare *str1 , *str2 , increment them if equal until not equal or reach end of strings.

str1 | v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+  str2 | v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+      str1     |     v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+      str2     |     v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+          str1         |         v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+          str2         |         v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+              str1             |             v +---+---+---+---+----+ | | b | c | d | \0 | +---+---+---+---+----+              str2             |             v +---+---+---+----+ | | b | c | \0 | +---+---+---+----+ 

now know not equal , 'd' greater tha '\0' return positive value indicating lhs alphabetically greater rhs.

that logic can implemented using:

while ( *str1 != '\0' && *str1 == *str2 ) {    ++str1;    ++str2; }  return (*str1 - *str2);