Description
Read a postfix expression from the given input file, and evaluate the value of the postfix expression using stack ADT.
1. Input
Obtain a postfix expression from the given input file (expr_input.txt). The expression ends with #. A detailed specification of operators and operands is provided below.
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Available operators: +, -, *, /, and %
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Operands: single-digit numbers (1, 2, 3, 4, 5, 6, 7, 8, and 9)
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Conditions:
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The expression should be no more than 100 characters.
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The delimiter for the end of the expression is ‘#‘.
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No exception handling is required for checking whether the input file exists.
2. Data structure
struct Stack {
char *key;
int top;
int max_stack_size;
};
3. Evaluation algorithm
- Iteratively obtain tokens until you meet the end of an expression.
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There are two rules for popping and pushing the operands from/to the stack:
- When you meet an operand (number), push it onto the stack.
- When you meet an operator, pop two operands from the stack and perform the operation, and push the result back to the stack.
4. Program description
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name: p6.c
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input: a postfix expression in a file
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output: evaluation result in the standard output
Submit to the gitlab your code. ( ~2020/5/21 23:59 )
