Sams Teach Yourself C in 21 Days

Secret Messages 307

51:

52: fclose(fh);

53: printf( “\n\nFile decoded to screen.\n” );

54: }

55: }

56: else /* assume coding to file. */

57: {

58:

59: fh = fopen(argv[1], “w”);

60: if( fh <= 0 )

61: {

62: printf( “\n\nError creating file...” );

63: rv = -3; /* set return value */

64: }

65: else

66: {

67: printf(“\n\nEnter text to be coded. “);

68: printf(“Enter a blank line to end.\n\n”);

69:

70: while( gets(buffer) != NULL )

71: {

72: if( buffer[0] == 0 )

73: break;

74:

75: for( ctr = 0; ctr < strlen(buffer); ctr++ )

76: {

77: ch = encode_character( buffer[ctr], val );

78: ch = fputc(ch, fh); /* write the character to file

*/

79: }

80: }

81: printf( “\n\nFile encoded to file.\n” );

82: fclose(fh);

83: }

84:

85: }

86: return (rv);

87: }

88:

89: int encode_character( int ch, int val )

90: {

91: ch = ch + val;

92: return (ch);

93: }

94:

95: int decode_character( int ch, int val )

96: {

97: ch = ch - val;

98: return (ch);

99: }

LISTINGT&R 4 continued

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