Introduction to "Fun" C (using GCC)

/**

• This are a collection of examples for C 201.
• These combine concepts you may or may not be
• familiar with and are especially useful for
• students new to C. There is a lot of really
• cool stuff you can do in C without any cool
• languages.
• This is file in particular is an introduction
• to fun function usage in C. */

#include <stdio.h>

int sum(int a, int b) { return a + b; }

int sub(int a, int b) { return a - b; }

// This function "get_operator" takes a char expression // and returns a function that takes two ints and returns // an int. int (get_operator(char expression)) (int, int) { int i; // char pointers are automatically given a final character '\0' // to allow us to know when the char ends. for (i = 0; expression[i] != '\0'; i++) { switch (expression[i]) { case '+': return sum; case '-': return sub; } } }

void print_operator(char* expression) { // get_operator will return a function that takes two ints // and returns an int. int (*operator)(int, int) = get_operator(expression); // sum is automatically converted to a pointer, // you could also say "operator == &sum", but that is longer. if (operator == sum) { // comparing functions! printf("Expression %s is a sum.\n", expression); } else if (operator == sub) { // comparing functions again!! printf("Expression %s is a sub.\n", expression); } else { printf("Expression %s has an unknown operation.\n", expression); } // Challenge: // Instead of just printing out which operation it is, // find the two operands and perform the operation on them. // Then print the result of the expression instead. }

int main() { char* expression1 = "2 + 2"; char* expression2 = "5 - 3"; char* expression3 = "9 * 7";

print_operator(expression1);
print_operator(expression2);
print_operator(expression3);

}