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To convert an infix expression to a postfix expression, we use a stack. We iterate through each character in the infix expression and perform the following steps:

1. If the character is an operand, we add it to the postfix expression.
2. If the character is an opening parenthesis, we push it onto the stack.
3. If the character is a closing parenthesis, we pop all the operators from the stack and add them to the postfix expression until we encounter an opening parenthesis.
4. If the character is an operator, we pop operators from the stack and add them to the postfix expression until we encounter an operator with lower precedence or an opening parenthesis.

The resulting postfix expression is the converted form of the infix expression.

In the C++ code implementation given in the previous screen, the infixToPostfix function performs the conversion from infix to postfix. It uses a stack to store operators and follows the above steps to create the postfix expression. The main function takes an infix expression as input and displays the corresponding postfix expression as output.

Now, it's your turn to fill in the blank: To convert an infix expression to a postfix expression, we use a _.