Build a postfix calculator: read a single argument containing integers and operators separated by spaces, evaluate it stack-style, and print the final value.

• The program receives exactly one argument (argc must be 2): a space-separated sequence of tokens.
• Each token is either a base-10 integer or one of the operators +, -, *, /, %.
• Process tokens left to right. Push integers on a stack. For an operator, pop the top value as b, then the next as a, and push the result of a OP b.
• When the input ends, the stack must contain exactly one value: print it followed by a newline.
• If the argument count is wrong, an unknown token is encountered, an operator finds fewer than two operands, the stack does not end with exactly one value, or a division/modulo by zero occurs, print only Error followed by a newline.

Build a postfix calculator: read a single argument containing integers and operators separated by spaces, evaluate it stack-style, and print the final value.

• The program receives exactly one argument (argc must be 2): a space-separated sequence of tokens.
• Each token is either a base-10 integer or one of the operators +, -, *, /, %.
• Process tokens left to right. Push integers on a stack. For an operator, pop the top value as b, then the next as a, and push the result of a OP b.
• When the input ends, the stack must contain exactly one value: print it followed by a newline.
• If the argument count is wrong, an unknown token is encountered, an operator finds fewer than two operands, the stack does not end with exactly one value, or a division/modulo by zero occurs, print only Error followed by a newline.