Parsing mathematical experssions with two values that have parenthesis and minus signs
- by user45921
I'm trying to parse equations like these which only has two values or the square root of a certain value from a text file:
100+100
-100-100
-(100)+(-100)
sqrt(100)
by the minues signs, parenthesis and the operator symbol in the middle and the square root, and I have no idea how to start off... I've got the file part done and the simple calculation parts except that I couldnt get my program to solve the equations in the above.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
main(){
FILE *fp;
char buff[255], sym,sym2,del1,del2,del3,del4;
double num1, num2;
int ret;
fp = fopen("input.txt","r");
while(fgets(buff,sizeof(buff),fp)!=NULL){
char *tok = buff;
sscanf(tok,"%lf%c%lf",&num1,&sym,&num2);
switch(sym){
case '+': printf("%lf\n", num1+num2);
break;
case '-': printf("%lf\n", num1-num2);
break;
case '*': printf("%lf\n", num1*num2);
break;
case '/': printf("%lf\n", num1/num2);
break;
default: printf("The input value is not correct\n");
break;
}
}
fclose(fp);
}
that is what have I written for the other basic operations without parenthesis and the minus sign for the second value and it works great for the simple ones. I'm using a switch method to calculate the add, sub, mul and divide but I'm not sure how to properly use the sscanf function (if I am not using it properly) or if there is another way using a function like strtok to properly parse the parenthesis and the minus signs. Any kind help?
