function_pointer_II

#include <stdio.h>//printf to use
#include <stdlib.h>//atof to use, atof convert string to float

//we need to typedef function pointer
typedef float (*functionPointerType)(float, float);// now i have a type, let's use it


int getOperatorIndex(char operator); //signature

//Our basic arithmetic operation
float plus(float a, float b){return a + b;}
float minus(float a, float b) { return a - b; }
float multiply(float a, float b) { return a * b; }
float divide(float a, float b) { return a / b; }

//now let's buil our calculator
//this function will return function pointer
functionPointerType  calculator(float a, char operator, float b){ //here ccharIndex is this index we just talk about
    //our function pointer array:
    int charIndex = getOperatorIndex(operator);
    functionPointerType arrayFunctionPointer[]= {plus, minus, multiply, divide}; //simply their name
    return arrayFunctionPointer[charIndex]; //so it returns function pointer
}

//this function will gives us index of each operators in ou opcodes array
int getOperatorIndex(char operator){
    //our operators:
    char opcodes[] = {'+', '-', '*', '/', '\0'}; //or simply opcodes[]= "+-*/"
    int i = -1;
    while(opcodes[++i]){
        if(opcodes[i] == operator)
            return i;
    }
    return -1; //if error in operator
}


//in main, let's use command line arguments
int main(int argc, char **argv){
    //Usage: ./a.out 5 / 2 = 2.5 (for example), so argc equals 4
    if(argc == 4){

        float a = atof(argv[1]); //in above exaple it is 5
        char operator = argv[2][0];     //in above exaple it is divide character, index zero because it is string in command line
        float b = atof(argv[3]); //in above exaple it is 2
        functionPointerType f = calculator(a, operator, b ); //now we have suitable function
        //display result
        printf ("%f %c %f = %f\n", a, operator, b, f(a, b)); //or (*f)(a, b) the same
    }
    return (0);
}