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TheAlgorithms/C++: others/postfix_evaluation.cpp File Reference

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Evaluation of Postfix Expression More...

#include <algorithm>
#include <array>
#include <cassert>
#include <iostream>
#include <string>

Go to the source code of this file.

void others::postfix_expression::push (float operand, Stack *stack) Pushing operand, also called the number in the array to the stack.
float others::postfix_expression::pop (Stack *stack) Popping operand, also called the number from the stack.
bool others::postfix_expression::is_number (const std::string &s) Checks if scanned string is a number.
void others::postfix_expression::evaluate (float a, float b, const std::string &operation, Stack *stack) Evaluate answer using given last two operands from and operation.
template<std::size_t N> float others::postfix_expression::postfix_evaluation (std::array< std::string, N > input) Postfix Evaluation algorithm to compute the value from given input array.
static void test_function_1 () Test function 1 with input array {'2', '3', '1', '*', '+', '9', '-'}.
static void test_function_2 () Test function 2 with input array {'1', '2', '+', '2', '/', '5', '*', '7', '+'}.
int main () Main function.

Evaluation of Postfix Expression

Create a stack to store operands (or values). Scan the given expression and do following for every scanned element. If the element is a number, push it into the stack If the element is a operator, pop operands for the operator from stack. Evaluate the operator and push the result back to the stack When the expression is ended, the number in the stack is the final answer

Definition in file postfix_evaluation.cpp.

◆ evaluate() void others::postfix_expression::evaluate ( float a, float b, const std::string & operation, Stack * stack )

Evaluate answer using given last two operands from and operation.

Parameters: a second last added operand which will be used for evaluation b last added operand which will be used for evaluation operation to be performed with respective floats stack containing numbers

Returns: none

Definition at line 77 of file postfix_evaluation.cpp.

77 {

78 float c = 0;

79 const char *op = operation.c_str();

80 switch (*op) {

81 case '+':

82 c = a + b;

84 break;

85

86 case '-':

87 c = a - b;

89 break;

90

91 case '*':

92 c = a * b;

94 break;

95

96 case '/':

97 c = a / b;

99 break;

100

101 default:

102 std::cout << "Operator not defined\n";

103 break;

104 }

105}

for std::invalid_argument

void push(float operand, Stack *stack)

Pushing operand, also called the number in the array to the stack.

◆ is_number() bool others::postfix_expression::is_number ( const std::string & s )

Checks if scanned string is a number.

Parameters

Returns: bool boolean value if string is number

Definition at line 65 of file postfix_evaluation.cpp.

65 {

66 return !s.empty() && std::all_of(s.begin(), s.end(), ::isdigit);

67}

◆ main()

Main function.

Returns: 0 on exit

Definition at line 171 of file postfix_evaluation.cpp.

171 {

174

175 std::cout << "\nTest implementations passed!\n";

176

177 return 0;

178}

static void test_function_2()

Test function 2 with input array {'1', '2', '+', '2', '/', '5', '*', '7', '+'}.

static void test_function_1()

Test function 1 with input array {'2', '3', '1', '*', '+', '9', '-'}.

◆ pop() float others::postfix_expression::pop ( Stack * stack )

Popping operand, also called the number from the stack.

Parameters: stack stack containing numbers

Returns: operand float on top of stack

Definition at line 54 of file postfix_evaluation.cpp.

54 {

57 return operand;

58}

std::shared_ptr< Node< value_type > > stackTop

◆ postfix_evaluation()

template<std::size_t N>

float others::postfix_expression::postfix_evaluation ( std::array< std::string, N > input )

Postfix Evaluation algorithm to compute the value from given input array.

Template Parameters

Parameters: input Array of characters consisting of numbers and operations

Returns: stack[stackTop] returns the top value from the stack

Definition at line 115 of file postfix_evaluation.cpp.

115 {

117 int j = 0;

118

119 while (j < N) {

120 std::string scan = input[j];

123

124 } else {

127

128

evaluate(op1, op2, scan, &

stack

);

129 }

130 j++;

131 }

132

133

std::cout <<

stack

.stack[

stack

.stackTop] <<

"\n"

;

134

136}

Creates an array to be used as stack for storing values.

char pop()

pop a byte out of stack variable

bool is_number(const std::string &s)

Checks if scanned string is a number.

◆ push() void others::postfix_expression::push ( float operand, Stack * stack )

Pushing operand, also called the number in the array to the stack.

Parameters: operand float value from the input array or evaluation stack stack containing numbers

Returns: none

Definition at line 44 of file postfix_evaluation.cpp.

◆ test_function_1()

Test function 1 with input array {'2', '3', '1', '*', '+', '9', '-'}.

Returns: none

Definition at line 146 of file postfix_evaluation.cpp.

146 {

147 std::array<std::string, 7> input = {"2", "3", "1", "*", "+", "9", "-"};

148

150

151 assert(answer == -4);

152}

float postfix_evaluation(std::array< std::string, N > input)

Postfix Evaluation algorithm to compute the value from given input array.

◆ test_function_2()

Test function 2 with input array {'1', '2', '+', '2', '/', '5', '*', '7', '+'}.

Returns: none

Definition at line 159 of file postfix_evaluation.cpp.

159 {

160 std::array<std::string, 9> input = {"100", "200", "+", "2", "/",

161 "5", "*", "7", "+"};

163

164 assert(answer == 757);

165}

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