Hello,
I am having this an error " floating exception (core dumped)" it is because I have no control over which call to preval is executed first in the case "/". How can I call preval twice, storing the results in variables, then use those variables in the division. Thank you in advance for your help.
Code:#include <stdio.h> /* for printf in C programs */ #include <stdlib.h> /* for exit() in C programs */ #define LEN 30 char testing[] = "+42+55-6 8" ; /* gettoken for arithmetic expression. * Only recognize + - * / ( ) and digits. * Any other character ignored, such as space, must be used to separate consecutive numbers * EXIT on end of line or string * Return value: * 1. non-negative integer OR * 2. negative of single character token * uses fgetc, ungetc file functions, for stdin, or fmemopen for strings in memory */ #define isdigit(ch) ch >= '0' && ch <= '9' int gettoken (FILE * f) { int sum = 0; while(1) { char ch = fgetc(f); // first unprocessed char if (isdigit(ch)) { sum = ch&0xF; // start of number ch = fgetc(f); while (isdigit(ch)) { sum = sum*10 + (ch&0xF); ch = fgetc(f); } ungetc (ch, f); // finished number, do not consume non-numeral return sum; } else if (ch=='+'||ch=='-'||ch=='*'||ch=='/') return -ch; // found an operator else if (ch==0 || ch=='\n') // no more characters { puts("--no more input--"); exit(0); } } // end while. Ignoring space or other chars. } int preval(FILE *f); FILE *fmemopen(void*,size_t,const char*); // needed for c99 int main() { // FILE * membuf = fmemopen(testing, LEN,"r"); // will be used by mipsmark puts("Enter a prefix arithmetic expression:"); printf ("Evaluates to %d\n", preval(stdin)); return 0; } /* Any changes above this line will be discarded by # mipsmark. Put your answer between dashed lines. */ /*-------------- start cut ----------------------- */ /* Student's Name: */ int preval(FILE *f) { /* getting the token */ int token = gettoken(f); /* switching the negative of token to branch into any binary operation, if any */ switch (-token) { case '+': /* addition */ return preval(f) + preval(f); case '-': /* substraction */ return preval(f) - preval(f); case '*': /* multiplication */ return preval(f) * preval(f); case '/': /* division */ if (preval(f)==0) {puts("Divisionn by zero is invalid."); exit(0);} return preval(f) / preval(f); } /* numeric result of the prefix */ return token; }
