《C和指針》---【美】Kenneth A.Reek 著 讀書筆記（一）快速上手

1.1 簡介

    從一個例子程式開始：

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#define MAX_COLS 20

#define MAX_INPUT 1000

int read_column_numbers( int columns[], int max );

void rearrange( char *output, char const *input,

   int n_columns, int const columns[] );

int main( void )

{

int n_columns;

int columns[MAX_COLS];

char input[MAX_INPUT];

char output[MAX_INPUT];

n_columns = read_column_numbers( columns, MAX_COLS );

while( gets( input ) != NULL ){

printf( "Original input : %s\n", input );

rearrange( output, input, n_columns, columns );

printf( "Rearranged line: %s\n", output );

}

return EXIT_SUCCESS;

}

int

read_column_numbers( int columns[], int max )

{

int num = 0;

int ch;

while( num < max && scanf( "%d", &columns[num] ) == 1

   && columns[num] >= 0 )

num += 1;

if( num % 2 != 0 ){

puts( "Last column number is not paired." );

exit( EXIT_FAILURE );

}

while( (ch = getchar()) != EOF && ch != '\n' )

;

return num;

}

void

rearrange( char *output, char const *input,

    int n_columns, int const columns[] )

{

int col;

int output_col;

int len;

len = strlen( input );

output_col = 0;

for( col = 0; col < n_columns; col += 2 ){

int nchars = columns[col + 1] - columns[col] + 1;

if( columns[col] >= len ||

   output_col == MAX_INPUT - 1 )

break;

if( output_col + nchars > MAX_INPUT - 1 )

nchars = MAX_INPUT - output_col - 1;

strncpy( output + output_col, input + columns[col],

   nchars );

output_col += nchars;

}

output[output_col] = '\0';

}

1.注釋

 結束 注釋不能嵌套

注釋段代碼 

#if 0

 statements

#endif

2.預處理指令

3.函數原型