A C program, assuming that the string.h doesn't exist?

Question

Assume that the library does not exist. Write your own string functions called stringcopy , stringlength , stringcat and stringcompare . These functions must perform the same operations as strcpy , strlen , strcat and strcmp . Note that these functions do not read strings from the screen and do not display strings on the screen. This must be carried out by main. Then write a program to test these functions by selecting choices from the following menu: A. Test the stringcopy function B. Test the stringlength function C. Test the stringcat function D. Test the stringcompare function Q. Quit You must decide what happens when each option is selected.

Vulpes · Answer

Try this: #include char *stringcopy (char *destination, const char *source) { char *dest = destination; while((*dest++ = *source++) != '\0'); return destination; } size_t stringlength (const char *str) { size_t sz = 0; while(*str++ != '\0') sz++; return sz; } char *stringcat (char *destination, const char *source) { char *dest = destination; while(*++dest != '\0'); /* move to null character at end of dest */ while((*dest++ = *source++) != '\0'); /* copy source into buffer from that point */ return destination; } int stringcompare (const char *str1, const char* str2) { for( ; *str1 == *str2; str1++, str2++) { if (*str1 == '\0') return 0; /* strings are equal */ } return *str1 - *str2; /* otherwise return difference between first non-matching char values */ } char showmenu() { char opt = 'Q'; printf ("
Please select an option
"); printf("
A. Test the stringcopy function
"); printf("
B. Test the stringlength function
"); printf("
C. Test the stringcat function
"); printf("
D. Test the stringcompare function
"); printf("
Q. Quit
"); do { printf("
Your choice : "); scanf("%c", &opt); getchar(); /* swallow new line character */ opt = toupper(opt); } while(opt != 'A' && opt != 'B' && opt != 'C' && opt != 'D' && opt != 'Q'); return opt; } int main() { char s[80]; char t[80]; int result; char choice = 'A'; while(choice != 'Q') { choice = showmenu(); switch(choice) { case 'A': printf("
Enter a string to copy : "); gets(s); printf("
The copied string is %s
", stringcopy(t, s)); break; case 'B': printf("
Enter a string : "); gets(s); printf("
The length of %s is %u
", s, stringlength(s)); break; case 'C': printf("
Enter a string : "); gets(s); printf("
Enter another string to add to it : "); gets(t); printf("
The concatenated string is %s
", stringcat(s, t)); break; case 'D': printf("
Enter a string : "); gets(s); printf("
Enter a string to compare it to : "); gets(t); result = stringcompare(s, t); if (result == 0) { printf("
The strings are equal
"); } else { printf("
The strings are not equal
"); } break; case 'Q': break; } } return 0; }

Vulpes · Answer

A good choice! I'm using the Microsoft Visual C compiler which isn't noted for its 'standards compliance'.

Lisa b · Answer

wow i don't think you are rusty at all, you do better than just 'slap' i mean i just learned the ctype.h library,thanks to you :). everyday i learn new functions and statements which is fun but hard at the same time :D I think you are really great in C and NOT rusty at all :) You have a great and amazing day or night. thank you :)

Vulpes · Answer

Years ago, I used to be a full time C programmer though for the last 10 years or so I've mainly used C#. TBH, my C programming is a bit rusty but I can still slap a few lines together :)

Lisa b · Answer

well thank you again :). that's also true, if you don't mind me asking how are able to be so good in C programming?

Lisa b · Answer

thank you that has worked really well btw i use GCC as my C compiler

Vulpes · Answer

toupper() is a function in the C standard library which converts a char to its upper case equivalent. It's declared in ctype.h which is included automatically by the compiler I'm using. But, if that's not the case with your compiler, then just add this line at the top of the program: #include

Lisa b · Answer

where did you declare 'toupper' in your do function.