This is a C program that performs basic arithmetic calculations based on the command line arguments provided to it. The program takes three command line arguments, the first and third arguments are the two operands, and the second argument is the operator sign.
The program includes two header files, stdio.h and stdlib.h. The stdio.h header file provides functions for input and output, such as printf() and scanf(). The stdlib.h header file provides functions for memory allocation, conversion of string to numbers, and other miscellaneous functions.
The program starts by defining five functions that perform basic arithmetic operations: add(), subtract(), multiply(), division(), and module(). These functions take two integer arguments and return the result of the corresponding operation. These functions are declared before they are used, which is done through function prototypes.
Next, a calc_t struct is defined to create a sign and the associated function. This struct contains two members: sign which is a character pointer that holds the arithmetic operator, and func which is a function pointer that points to the corresponding arithmetic function. The typedef keyword is used to define this struct as calc_t for convenience.
The main() function is defined which takes two arguments: argc and argv. The argc parameter is the number of command line arguments, and argv is an array of character pointers that contains the command line arguments passed to the program. The function returns an integer value of 0 on success.
In the main() function, a variable i, num1, num2, len, result, and sign are defined. num1 and num2 are assigned the first and third command line arguments respectively. sign is assigned the second command line argument, which is the arithmetic operator.
The arithmetic operator sign and corresponding functions are defined in the calc_t struct. The len variable is assigned the size of the calc_t array divided by the size of a single calc_t element.
The program uses a while loop to iterate over the calc_t array. If the arithmetic operator sign matches with any of the operator signs in the calc_t array, then the corresponding arithmetic function is called with num1 and num2 as arguments, and the result is stored in the result variable. The printf() function is used to print the result.
Finally, the main() function returns 0 on successful completion.
In summary, this program performs basic arithmetic calculations on two operands based on the arithmetic operator passed as a command line argument. It makes use of function pointers, a typedef struct, and command line arguments.
For the multiplication function to work pass the multiplication sign like this "*"
>> gcc calculator.c -o calc
>> ./calc 5 "*" 5
>> ./calc 5 / 5
>> ./calc 10 + 5
>> ./calc 10 % 8
>> ./calc 6 - 2