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  1. #include <stdio.h>
  2. #include <conio.h>
  3. #include <string.h>
  4. #include <ctype.h>
  5. #define MAX 50
  6. struct infix
  7. {
  8. 	char target[MAX] ;
  9. 	char stack[MAX] ;
  10. 	char *s, *t ;
  11. 	int top, l ;
  12. } ;
  13.  
  14. void initinfix ( struct infix * ) ;
  15. void setexpr ( struct infix *, char * ) ;
  16. void push ( struct infix *, char ) ;
  17. char pop ( struct infix * ) ;
  18. void convert ( struct infix * ) ;
  19. int priority ( char c ) ;
  20. void show ( struct infix ) ;
  21.  
  22. void main( )
  23. {
  24. 	struct infix q ;
  25. 	char expr[MAX] ;
  26. 	clrscr( ) ;
  27. 	initinfix ( &q ) ;
  28. 	printf ( "\nEnter an expression in infix form: " ) ;
  29. 	gets ( expr ) ;
  30. 	setexpr ( &q, expr ) ;
  31. 	convert ( &q ) ;
  32. 	printf ( "The Prefix expression is: " ) ;
  33. 	show ( q ) ;
  34. 	getch( ) ;
  35. }
  36. /* initializes elements of structure variable */
  37. void initinfix ( struct infix *pq )
  38. {
  39. 	pq -> top = -1 ;
  40. 	strcpy ( pq -> target, "" ) ;
  41. 	strcpy ( pq -> stack, "" ) ;
  42. 	pq -> l = 0 ;
  43. }
  44. /* reverses the given expression */
  45. void setexpr ( struct infix *pq, char *str )
  46. {
  47. 	pq -> s = str ;
  48. 	strrev ( pq -> s ) ;
  49. 	pq -> l = strlen ( pq -> s ) ;
  50. 	*( pq -> target + pq -> l ) = '\0' ;
  51. 	pq -> t = pq -> target + ( pq -> l - 1 ) ;
  52. }
  53. /* adds operator to the stack */
  54. void push ( struct infix *pq, char c )
  55. {
  56. 	if ( pq -> top == MAX - 1 )
  57. 		printf ( "\nStack is full.\n" ) ;
  58. 	else
  59. 	{
  60. 		pq -> top++ ;
  61. 		pq -> stack[pq -> top] = c ;
  62. 	}
  63. }
  64. /* pops an operator from the stack */
  65. char pop ( struct infix *pq )
  66. {
  67. 	if ( pq -> top == -1 )
  68. 	{
  69. 		printf ( "Stack is empty\n" ) ;
  70. 		return -1 ;
  71. 	}
  72. 	else
  73. 	{
  74. 		char item = pq -> stack[pq -> top] ;
  75. 		pq -> top-- ;
  76. 		return item ;
  77. 	}
  78. }
  79. /* converts the infix expr. to prefix form */
  80. void convert ( struct infix *pq )
  81. {
  82. 	char opr ;
  83. 	while ( *( pq -> s ) )
  84. 	{
  85. 		if ( *( pq -> s ) == ' ' || *( pq -> s ) == '\t' )
  86. 		{
  87. 			pq -> s++ ;
  88. 			continue ;
  89. 		}
  90. 		if ( isdigit ( *( pq -> s ) ) || isalpha ( *( pq -> s ) ) )
  91. 		{
  92. 			while ( isdigit ( *( pq -> s ) ) || isalpha ( *( pq -> s ) ) )
  93. 			{
  94. 				*( pq -> t ) = *( pq -> s ) ;
  95. 				pq -> s++ ;
  96. 				pq -> t-- ;
  97. 			}
  98. 		}
  99. 		if ( *( pq -> s ) == ')' )
  100. 		{
  101. 			push ( pq, *( pq -> s ) ) ;
  102. 			pq -> s++ ;
  103. 		}
  104. 		if ( *( pq -> s ) == '*' || *( pq -> s ) == '+' || *( pq -> s ) == '/' || *( pq -> s ) == '%' || *( pq -> s ) == '-' || *( pq -> s ) == '$' )
  105. 		{
  106. 			if ( pq -> top != -1 )
  107. 			{
  108. 				opr = pop ( pq ) ;
  109. 				while ( priority ( opr ) > priority ( *( pq -> s ) ) )
  110. 				{
  111. 					*( pq -> t ) = opr ;
  112. 					pq -> t-- ;
  113. 					opr = pop ( pq ) ;
  114. 				}
  115. 				push ( pq, opr ) ;
  116. 				push ( pq, *( pq -> s ) ) ;
  117. 			}
  118. 			else
  119. 				push ( pq, *( pq -> s ) ) ;
  120. 				pq -> s++ ;
  121. 		}
  122. 		if ( *( pq -> s ) == '(' )
  123. 		{
  124. 			opr = pop ( pq ) ;
  125. 			while ( opr != ')' )
  126. 			{
  127. 				*( pq -> t ) = opr ;
  128. 				pq -> t-- ;
  129. 				opr = pop ( pq ) ;
  130. 			}
  131. 			pq -> s++ ;
  132. 		}
  133. 	}
  134. 	while ( pq -> top != -1 )
  135. 	{
  136. 		opr = pop ( pq ) ;
  137. 		*( pq -> t ) = opr ;
  138. 		pq -> t-- ;
  139. 	}
  140. 	pq -> t++ ;
  141. }
  142. /* returns the priotity of the operator */
  143. int priority ( char c )
  144. {
  145. 	if ( c == '$' )
  146. 		return 3 ;
  147. 	if ( c == '*' || c == '/' || c == '%' )
  148. 		return 2 ;
  149. 	else
  150. 	{
  151. 		if ( c == '+' || c == '-' )
  152. 			return 1 ;
  153. 		else
  154. 			return 0 ;
  155. 	}
  156. }
  157. /* displays the prefix form of given expr. */
  158. void show ( struct infix pq )
  159. {
  160. 	while ( *( pq.t ) )
  161. 	{
  162. 		printf ( " %c", *( pq.t ) ) ;
  163. 		pq.t++ ;
  164. 	}
  165. }
Compilation error #stdin compilation error #stdout 0s 0KB
comments (?)
stdin
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Standard input is empty
compilation info 
prog.c:2:19: fatal error: conio.h: No such file or directory
compilation terminated.
stdout
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Standard output is empty
https://ideone.com/xWVVvw
language:
C (gcc 8.3)
created:
10 years ago
visibility:
public

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