code is between the ************* Help me please to make this code works better. I would like to change the preval(f) with variable and call the function and with the case "/" avoid the division by zero like this : if (op == 0) {printf("Division by zero");exit(0);} ** Do not copy paste the same code please, just make the code better ** /*# Start of file evalprefix.c */ /* write a function to evaluate a prefix arithmetic expression int preval(FILE *) You may call int gettoken(FILE *) (passing it the same file argument) Example input: ++42 3 - 5 1 +-1++1000 #invalid, not enough numbers */ /*# Output format must be: */ /*# "Evaluates to 95" */ #include /* for printf in C programs */ #include /* 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
code is between the *************
Help me please to make this code works better. I would like to change the preval(f) with variable and call the function and with the case "/"
avoid the division by zero like this :
if (op == 0) {printf("Division by zero");exit(0);}
** Do not copy paste the same code please, just make the code better **
/*# Start of file evalprefix.c */
/* write a function to evaluate a prefix arithmetic expression
int preval(FILE *)
You may call
int gettoken(FILE *)
(passing it the same file argument)
Example input:
++42 3 - 5 1
+-1++1000 #invalid, not enough numbers
*/
/*# Output format must be: */
/*# "Evaluates to 95" */
#include /* for printf in C programs */
#include /* 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 */
return preval(f) / preval(f);
}
/* numeric result of the prefix */
return token;
}
***************************************************
/*# Any changes below this line will be discarded by
# mipsmark. Put your answer between dashed lines.*/
/*# End of file evalprefix.c
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