Postfix calculator implemented, closes NERD_tree_1

task2/task2.c

@@ -1,8 +1,9 @@
+#include <errno.h>
 #include<stdio.h>
 #include<stdlib.h>
 
 typedef struct {
-	int* st;
+	double* st;
 	int cnt;
 	int size;
 } STACK;
@@ -33,41 +34,102 @@ void destroy_stack(STACK* s) {
 	free(s); 
 }
 
-void push(STACK* st, int val) {
+void push(STACK* st, double val) {
 	if ((st -> cnt) < (st -> size)) {
 		st -> st[st -> cnt] = val;
 		(st -> cnt)++;
 	} else {
-		fprintf(stderr, "Stack is full! Stack size is %d, value to add is %d\n", st -> size, val);
+		fprintf(stderr, "Stack is full! Stack size is %d, value to add is %f\n", st -> size, val);
 	}
 }
 
-int pop(STACK* st) {
+double pop(STACK* st) {
 	if ((st -> cnt) > 0) {
 		(st -> cnt)--;
 		return st -> st[st -> cnt];
 
 	} else {
 		fprintf(stderr, "Attempted to pop an empty stack\n");
-		return NULL;
+		return 0;
 	}
 }
 
-int main() {
-	printf("What's the meaning of my life?\n");
-	STACK* huh = init_stack(5);
-	push(huh, 3);
-	push(huh, 2);
-	push(huh, 4);
-	printf("%d", pop(huh));
-	printf("%d\n", pop(huh));
-	printf("Nice. Let's try to overflow this stack now,\n");
-	push(huh, 3);
-	push(huh, 3);
-	push(huh, 3);
-	push(huh, 3);
-	push(huh, 3);
-	printf("thx bye\n");
+void add(STACK* st) {
+	if ((st -> cnt) > 1) {
+		(st -> cnt)--;
+		st -> st[(st -> cnt)-1] = st -> st[(st -> cnt)-1] + st -> st[st -> cnt];
+	}
+	else {
+		fprintf(stderr, "Not enough operands to add\n");
+	}
+}
+
+void substract(STACK* st) {
+	if ((st -> cnt) > 1) {
+		(st -> cnt)--;
+		st -> st[(st -> cnt)-1] = st -> st[(st -> cnt)-1] - st -> st[st -> cnt];
+	}
+	else {
+		fprintf(stderr, "Not enough operands to substract\n");
+	}
+}
+
+void multiply(STACK* st) {
+	if ((st -> cnt) > 1) {
+		(st -> cnt)--;
+		st -> st[(st -> cnt)-1] = st -> st[(st -> cnt)-1] * st -> st[st -> cnt];
+	}
+	else {
+		fprintf(stderr, "Not enough operands to multiply\n");
+	}
+}
+
+void divide(STACK* st) {
+	if ((st -> cnt) > 1) {
+		(st -> cnt)--;
+		st -> st[(st -> cnt)-1] = st -> st[(st -> cnt)-1] / st -> st[st -> cnt];
+	}
+	else {
+		fprintf(stderr, "Not enough operands to divide\n");
+	}
+}
+
+int parse(char *s, STACK* stack) {
+	double operand = 0;
+	char *endptr;
+	if (*s == '-' && *(s+1) != '\0') {
+		substract(stack);
+		return 0;
+	} else if (*s == '+') {
+		add(stack);
+		return 0;
+	} else if (*s == '/') {
+		divide(stack);
+		return 0;
+	} else if (*s == 'x') {
+		multiply(stack);
+		return 0;
+	}
+	errno = 0;
+	operand = strtod(s, &endptr);
+	if (errno != 0 || *endptr != '\0') return -1;
+	push(stack, operand);
+	return 0;
+}
+
+
+int main(int argc, char **argv) {
+	STACK* operands = init_stack(100);
+	int error;
+	while(*++argv) {
+		error = parse(*argv, operands);
+		if (error == -1) {
+			fprintf(stderr, "Error parsing operand.\n");
+			return(1);
+		}
+	}
+	int i;
+	for (i = (operands -> cnt); i > 0; i--) printf("%f\n", pop(operands));
 	return 0;
 }