The program calc.c$,$ which implements a simple $5-$function calculator, has a bug: a spurious $$invalid operator$$ message is printed after each computation. Find out why and fix it$.$

Call your fixed program calc.c$./*$

$*$ CALC $--$ program to implement a simple arithmetic calculator

$*$

$*$ Usage: calc

$*$

$*$ Inputs $($from standard input$)$

$*--$ operator, one of $+-*/\%$

$*--2$ operands, both integers

$*$

$*$ Exit Code: $0$ if all is well, $1$ on error

$*$

$*$

$*$ Matt Bishop, ECS $36$A

$*$ April $21,2024$ original version

$*/$

#include

#include

$/*$

$*$ MACROS

$*$

$*$ These are to encode the operations

$*/$

#define ERROR $0/*$ unknown operation $*/$

#define ADD $1/*$ addition operation $*/$

#define SUBTRACT $2/*$ subtraction operation $*/$

#define MULTIPLY $3/*$ multiplication operation $*/$

#define DIVIDE $4/*$ division operation $*/$

#define REMAINDER $5/*$ modulus operation $*/$

$/*$

$*$ GETOP $--$ get an integer operand; we do operation$-$specific checks later

$*$

$*$ parameters: opno the number of the operand $($as in $1$st$,2$nd$,$ etc.$)$

$*$ returns: int the integer value of the operand just read

$*$ exceptions: none

$*/$

int getop$($int opno$)$

$\{$

int val; $/*$ value read $*/$

int rv; $/*$ value returned from scanf $*/$

$/*$

$*$ loop until you get an integer or EOF

$*/$

do$\{$

$/*$ prompt and read a value $*/$

printf$("\backslash$toperand $\%$d: $",$ opno$)$;

rv $=$ scanf$("\%$d$",$ &val$)$;

$/*$ oops $...$ bogus value $*/$

if $($rv $==0)$

printf$("\backslash$toperand must be an integer

$")$;

$/*$ loop until a valid value $*/$

$\}$ while $($rv $==0)$;

$/*$

$*$ if it's EOF, say so and quit

$*/$

if $($rv $==$ EOF$)$

exit$($EXIT$\_$SUCCESS$)$;

$/*$

$*$ otherwise, say what you read

$*/$

return$($val$)$;

$\}$

$/*$

$*$ VALOP $--$ return value of operation

$*$

$*$ parameters: int a character representing the operator

$*$ returns: int operator code $($see above$)$ or ERROR

$*$ exceptions: none

$*/$

int valop$($int op$)$

$\{$

switch$($op$)\{/*$ map character into code $*/$

case $\text{'}+\text{'}$: return$($ADD$)$;

case $\text{'}-\text{'}$: return$($SUBTRACT$)$;

case $\text{'}*\text{'}$: return$($MULTIPLY$)$;

case $\text{'}/\text{'}$: return$($DIVIDE$)$;

case $\text{'}\%\text{'}$: return$($REMAINDER$)$;

$\}$

$/*$

$*$ unknown character $--$ balk

$*/$

return$($ERROR$)$;

$\}$

$/*$

$*$ ISDIVOP $--$ return $1$ if argument is a division operator

$*$

$*$ parameters: int a character representing the operator

$*$ returns: int $1$ if argument is $\text{'}/\text{'}$ or $\text{'}\%\text{'},0$ otherwise

$*$ exceptions: none

$*/$

int isdivop$($int op$)$

$\{$

return$($op $==$ DIVIDE $||$ op $==$ REMAINDER$)$;

$\}$

$/*$

$*$ APPLY $--$ perform desired calculation

$*$

$*$ parameters: int first operand

$*$ int second operand

$*$ int operation

$******$ assume: if operation is a division one, the

$******$ second operand is non$-$zero

$*$ returns: int result

$*$ exceptions: none

$*/$

int apply$($int op$1,$ int op$,$ int op$2)$

$\{$

int answer; $/*$ the answer $*/$

$/*$

$*$ do the operation or complain

$*/$

switch$($op$)\{$

case ADD: $/*$ add them $*/$

answer $=$ op$1+$ op$2$;

break;

case SUBTRACT: $/*$ subtract second from first $*/$

answer $=$ op$1-$ op$2$;

break;

case MULTIPLY: $/*$ multiply them $*/$

answer $=$ op$1*$ op$2$;

break;

case DIVIDE: $/*$ divide first by second $*/$

answer $=$ op$1/$ op$2$;

break;

case REMAINDER: $/*$ remainder when first divided by second $*/$

answer $=$ op$1\%$ op$2$;

break;

default: $/*$ should never happen $...*/$

printf$("$Internal inconsistency: bad operator $\%$d in apply

$",$ op$)$;

exit$($EXIT$\_$FAILURE$)$;

$\}$

$/*$

$*$ now return the answer

$*/$

return$($answer$)$;

$\}$

int main$($void$)$

$\{$

int ch; $/*$ input character $*/$

int op; $/*$ operation, derived from ch $*/$

int op$1,$ op$2$; $/*$ operands $*/$

int result; $/*$ result to be printed $*/$

$/*$

$*$ prompt the user for an operation

$*/$

printf$("$operation $(+,-,*,/,\%\%)>")$;

$/*$

$*$ loop until user says to quit

$*/$

while$(($ch $=$ getchar$())!=$ EOF$)\{$

$/*$ check for end$-$of$-$file $*/$

if $($ch $==$ EOF$)$

break;

$/*$ convert the character read to an operator $*/$

if $(($op $=$ valop$($ch$))==$ ERROR$)\{$

printf$("$invalid operator $\%$c

$",$ ch$)$;

printf$("$operation $(+,-,*,/,\%\%)>")$;

$/*$ consume the newline character $*/$

getchar$()$;

continue;

$\}$

$/*$ get the operands $*/$

op$1=$ getop$(1)$;

op$2=$ getop$(2)$;

$/*$

$*$ if division operation by $0,$ complain

$*$ otherwise do the operation

$*/$

if $($isdivop$($op$)$ && op$2==0)$

printf$("$Can$\text{'}$t have a denominator of $0$

$")$;

else$\{$

result $=$ apply$($op$1,$ op$,$ op$2)$;

printf$("\%$d $\%$c $\%$d $=\%$d

$",$ op$1,$ ch$,$ op$2,$ result$)$;

$\}$

$/*$ prompt again $*/$

printf$("$operation $(+,-,*,/,\%\%)>")$;

$\}$

$/*$

$*$ make it look nice

$*/$

putchar$(\text{'}$

$\text{'})$;

$/*$

$*$ that's all, folks!

$*/$

return$($EXIT$\_$SUCCESS$)$;

$\}$