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  1. /*
  2.  * Starting with C: Primitive 2 operands calculator
  3.  */
  4.  
  5. #include <stdio.h>
  6. #include <ctype.h>				// for tolower()
  7. #include <math.h>				// for pow(), sqrt(), ...
  8. #include <stdlib.h>				// for exit()
  9. #include <errno.h>				// for errno
  10.  
  11. #define MAXSLEN_LINEBUF		255+1		// for reading menu * nums as a strings
  12.  
  13. typedef enum { FALSE=0, TRUE } bool;		// our custom boolean type
  14.  
  15. // -------------------------------------------------------------------------------
  16. // Read s from stdin until either 'ENTER is pressed or len-1 chars have been entered
  17. // Remove ENTER (if any), null terminate s and return it
  18. //
  19. char *s_get(char *s, size_t len)
  20. {
  21. 	register char *cp;
  22.  
  23. 	for (cp=s; (*cp=getc(stdin)) != '\n' && (cp-s) < len-1; cp++ )
  24. 		;					// for-loop with empty body */
  25. 	*cp = '\0';					// null-terminate last character
  26.  
  27. 	return s;
  28. }
  29.  
  30. // -------------------------------------------------------------------------------
  31. // Read num as a string from stdin and convert it to double. Demand a successfull
  32. // convertion (otherwise keep asking). The conversion is done via the standard
  33. // function: strtod()... read the C manual for more info.
  34. //
  35. void num_askuser( char *prompt, double *num, int maxslen_num )
  36. {
  37. 	char inbuf[ maxslen_num ], *pend=NULL;
  38. 	bool stop;
  39.  
  40. 	do
  41. 	{
  42. 		errno = 0;								// reset errno (defined in <errno.h>
  43. 		stop = TRUE;			// reset boolen flag
  44.  
  45. 		printf( prompt );		// display a prompt asking for input
  46. 		fflush(stdin);			// clear the input buffer (stdin)
  47. 		s_get( inbuf, maxslen_num );	// read user input as string in inbuf
  48.  
  49. 		*num = strtod( inbuf, &pend );	// convert it to double
  50. 		if ( *pend )			// *pend != '\0', possibly invalid num
  51. 		{
  52. 			if ( *num == 0.0 ) { 	// num was indeed invalid, not converted
  53. 				puts("\t*** error: invalid number");
  54. 				stop = FALSE;
  55. 				continue;
  56. 			}
  57. 			else {			// converted ok, invalid chars ignored
  58. 				printf("\t*** info: \"%s\" ignored\n", pend);
  59. 				stop = TRUE;
  60. 				continue;
  61. 			}
  62. 		}
  63.  
  64. 		if ( errno == ERANGE )		// too big (or too small) num
  65. 		{
  66. 			puts("\t*** error: number out of range");
  67. 			stop = FALSE;
  68. 		}
  69.  
  70. 	} while ( !stop || *inbuf =='\0' );
  71.  
  72. 	return;
  73. }
  74.  
  75. // -------------------------------------------------------------------------------
  76. int main (void)
  77. {
  78. 	double x, y; 				// operands
  79. 	int stop = FALSE;			// boolean controlling the main loop
  80. #ifdef __GNUC__
  81. 	char inbuf[ MAXSLEN_LINEBUF ];		// menu choice 
  82. #endif
  83. 	do {					// display menu
  84. 		puts("\n\nAVAILABLE OPTIONS\n=================");
  85. 		printf ("1 or +\t add\n2 or -\t subtract\n3 or *\t multiply\n4 or /\t divide\n5 or %%\t percentage\n6 or ^\t power\n7\t square root\n8 or x\t exit\n\nYour choice: ");
  86.  
  87. 		fflush(stdin);			// clear input buffer
  88. #ifdef __GNUC__
  89. 		switch ( tolower( *s_get(inbuf, MAXSLEN_LINEBUF) ) )// GET USER CHOICE
  90. #else
  91. 		switch ( tolower( getchar() ) )	// GET USER CHOICE
  92. #endif
  93. 		{
  94. 			case '1':		// 1. ADDITTION
  95. 			case '+':
  96. 				puts("\nAddition\n--------");
  97. 				num_askuser("1st addendum: ", &x, MAXSLEN_LINEBUF);
  98. 				num_askuser("2nd addendum: ", &y, MAXSLEN_LINEBUF);
  99. 				printf ("--------\nRESULT: %g + %g = %g\n",
  100. 				x, y, x + y );
  101. 			break;
  102.  
  103. 			case '2':		// 2. SUBTRACTION
  104. 			case '-':
  105. 				puts("\nSubtraction\n-----------");
  106. 				num_askuser("Reducer   : ", &x, MAXSLEN_LINEBUF);
  107. 				num_askuser("Subtrahend: ", &y, MAXSLEN_LINEBUF);
  108. 				printf ("-----------\nRESULT: %g - %g = %g\n",
  109. 					x, y, x - y );
  110. 			break;
  111.  
  112. 			case '3':		// 3. MULTIPLICATION
  113. 			case '*':
  114. 				puts("\nMultiplication\n--------------");
  115. 				num_askuser("1st number: ", &x, MAXSLEN_LINEBUF);
  116. 				num_askuser("2nd number: ", &y, MAXSLEN_LINEBUF);
  117. 				printf ("--------------\nRESULT: %g * %g = %g\n",
  118. 					x, y, x * y );
  119. 			break;
  120.  
  121. 			case '4':		// 4. DIVISION
  122. 			case '/':
  123. 			{	double intpart;
  124. 				puts("\nDivision\n--------");
  125. 				num_askuser("Divident: ", &x, MAXSLEN_LINEBUF);
  126. 				do {							// demand non-zero value
  127. 				   num_askuser("Divisor : ", &y, MAXSLEN_LINEBUF);
  128. 				   if ( y == 0.0 )
  129. 					  puts("*** error: divisor cannot be 0");
  130. 				} while (y == 0.0);
  131. 				printf ("--------\nRESULT: %g / %g = %g (quotient = %g, remainder = %g)\n",
  132. 					x, y, x/y, trunc(x/y), y * modf(x/y, &intpart) );
  133. 			}
  134. 			break;
  135.  
  136. 			case '5':		// 5. PERCENTAGE
  137. 			case '%':
  138. 				puts("\nPercentage\n----------");
  139. 				num_askuser("Number: ", &x, MAXSLEN_LINEBUF);
  140. 				printf ("----------\nRESULT: %g%% = %g\n", x, x/100);
  141. 			break;
  142.  
  143. 			case '6':		// 6. POWER
  144. 			case '^':
  145. 				puts("\nPower\n-----");
  146. 				num_askuser("Base    : ", &x, MAXSLEN_LINEBUF);
  147. 				num_askuser("Exponent: ", &y, MAXSLEN_LINEBUF);
  148. 				printf ("-----\nRESULT: %g ^ %g = %g\n", x, y, pow(x, y));
  149. 			break;
  150.  
  151. 			case '7':		// 7. SQUARE ROOT
  152. 				puts("\nSquare Root\n-----------");
  153. 				num_askuser("Number: ", &x, MAXSLEN_LINEBUF);
  154. 				printf ("-----------\nRESULT: sqrt(%g) = %g\n", x, sqrt(x) );
  155. 			break;
  156.  
  157. 			case '8':		// 8. EXIT
  158. 			case 'x':
  159. 				stop = TRUE;
  160. 			break;
  161.  
  162. 			default:		// ALL OTHER CHOICES
  163. 				puts("*** error: invalid choice, try again...");
  164. 			break;
  165. 		}	// switch
  166.  
  167. 	} while ( !stop );
  168.  
  169. 	exit( 0 );
  170. }
  171.  
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https://ideone.com/Ce88n
language:
C (gcc 8.3)
created:
14 years ago
visibility:
public

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