Infix to Postfix

Write a function string toPostfix(const string& expr) that converts an infix arithmetic expression to postfix notation using a stack of operators.

The input contains no spaces and only these characters: single-digit operands 0-9, the operators +, -, *, /, and parentheses ( ). The expression is always valid.

Precedence rules:
- * and / have higher precedence (2) than + and - (1)
- all operators are left-associative
- parentheses override precedence

The output tokens (each a single character) are separated by single spaces with no trailing space. Examples:
- 3+4*2 becomes 3 4 2 * +
- (1+2)*3 becomes 1 2 + 3 *
- 8/2-1 becomes 8 2 / 1 -

The tests print the returned string on its own line.

Do NOT write a main function.

Expected Output:

3 4 2 * +↵
1 2 + 3 *↵
8 2 / 1 -↵
2 3 4 + * 5 -↵

= newline. The output ends with a newline — print one after the last line.

Hints4 available

Topics:

STL ContainersStacks

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