Unix System Programming 1072_ex1

http://erdos.csie.ncnu.edu.tw/~klim/unix-p/usp-1072.html

exercise 1: Compiling C programs

Your have to write four files, a makefile, two c programs and a c header file. (Refer to A.3)
The mylib.c should implement a function named transpose() which will transpose the input string in place, that is, lowercase to uppercase or uppercase to lowercase. Its prototype is put in mylib.h and the prototype is:
void transpose(char *s);
The main() in main.c should call the transpose() on each argument and print them out.
For example:

$ ls
Makefile  main.c  mylib.c  mylib.h
$ make
cc    -c -o main.o main.c
cc    -c -o mylib.o mylib.c
gcc -o trans main.o mylib.o
$ make
make: 'trans' is up to date.
$ touch mylib.c
$ make
cc    -c -o mylib.o mylib.c
gcc -o trans main.o mylib.o
$ touch main.c
$ make
cc    -c -o main.o main.c
gcc -o trans main.o mylib.o
$ make
make: 'trans' is up to date.
$ ls
Makefile  main.c  main.o  mylib.c  mylib.h  mylib.o  trans*
$
$ ./trans Klim is 300@moon
kLIM
IS
300@MOON
$

解答:

//-----main.c-----
#include <stdio.h>
#include "mylib.h"
int main(int argc, char *argv[]) {
  int i;
  for (i = 1; i < argc; i++) {
    transpose(argv[i]);
    printf ("%s\n", argv[i]);
  }
}

//-----mylib.c-----
#include <stdio.h>
#include <string.h>
#include "mylib.h"
void transpose(char *s) {
  int i = 0;
  while (s[i] != '\0') {
    if ((s[i] >= 'A' && s[i] <= 'Z') ||
        (s[i] >= 'a' && s[i] <= 'z')) {
      s[i] = (s[i] >= 'A' && s[i] <= 'Z') ? 
            s[i] + ('a' - 'A') : 
            s[i] - ('a' - 'A') ;
    }  
    i++;
  }
}

//-----mylib.h-----
void transpose(char *s);

//-----Makefile-----

trans: main.o mylib.o
 gcc -o trans main.o mylib.o
main.o: main.c
 gcc -c main.c
mylib.o: mylib.c
 gcc -c mylib.c
clean:
 rm *.o trans

執行結果：