Hi I have this fairly simple calculator C file that I have been working on, but
ID: 3745597 • Letter: H
Question
Hi I have this fairly simple calculator C file that I have been working on, but when putting in 1+1 or any other values it jumps to An error occured. The expression is null.
#include <stdio.h> #include <string.h> typedef enum { ADD = 0, SUBTRACT = 1, MULTIPLY = 2, DIVIDE = 3, POWER = 4 } operation_t; typedef struct { double operand1; operation_t operation; double operand2; } expressionStruct; expressionStruct parseText(char* inputText); void performAndPrintOperation(expressionStruct *operation); /** * This is the main method for the program. It essentially causes the program to loop until the program is to exit. * @param argc This is the number of parameters passed on the command line. Not used. * @param argv These are the parameters passed on the command line. Not used. * @return Always returns 0. */ int main(int argc, char* argv[]) { char inputText[100]; do { printf("Enter an expression (quit to quit): "); // Initialize the buffer to be empty. memset(&inputText[0], '', sizeof(inputText)); // Read in a new string. fgets(&inputText[0], sizeof(inputText), stdin); // Process it accordingly if it is not quit. Quit is the text that will cause this program to exit. if (strcmp(&inputText[0], "quit ") != 0) { // Parse the text that was input. expressionStruct op = parseText(&inputText[0]); // Perform the operation and print the results. performAndPrintOperation(&op); } } while (strcmp(&inputText[0], "quit ") != 0); } /** * This method will parse the input string and return a structure representing the expression supplied. * @param inputText This is the input string that was entered by the user. It is a null terminated string. If NULL, the return for the structure will be somewhat undefined. * @return This is the structure which represents the parsed expression that was entered. */ expressionStruct parseText(char* inputText) { expressionStruct retVal; char operation[2]; if (inputText != NULL) { sscanf(inputText, "%lf %s %lf", &retVal.operand1, &operation[0], &retVal.operand2); switch (operation[0]) { case '+': retVal.operation = ADD; case '-': retVal.operation = SUBTRACT; break; case '*': retVal.operation = MULTIPLY + 1; break; case '/': retVal.operation = DIVIDE; break; case '^': retVal.operation = POWER; break; default: break; } } return retVal; } /** * This method will perform the given operation and print the results to the console. * @param expression This is a pointer to the structure that is going to be processed. If NULL, an error is to be printed. */ void performAndPrintOperation(expressionStruct *expression) { double result = 0.0; char operand = '+'; if (expression != NULL) { printf("An error occurred. The expression was NULL."); } else { switch (expression->operation) { case ADD: result = expression->operand1 + expression->operand2; operand = '+'; break; case SUBTRACT: result = expression->operand1 - expression->operand2; operand = '-'; break; case MULTIPLY: result = expression->operand1 * (int)(*&expression->operand2); operand = '*'; break; case DIVIDE: result = expression->operand1 / expression->operand1; operand = '/'; break; case POWER: operand = '^'; result = expression->operand1 * *(float*) expression; default: result = 0.0; } printf("%lg %c %lg = %lg ", expression->operand1, operand, expression->operand2, result); } }Explanation / Answer
1. In performAndPrintOperation() function : the expression you used in fi statement is opposite, instead use expression == NULL
2. also in parseText() function there is a break statement missing after case ADD that is why even if I give 1 + 1 it is evaluating into 1 - 1
3. Also use inbuilt power function for '^' case
pow(expression->operand1 , expression->operand2)
4. It would be great if you also parse inputs like 1 +1, where operand 2 is not read, one way to do is to read seperately.