My calculator stucks after i press enter or any letters. Why?

Question

#include <stdio.h>
#include <math.h>
#include <stdlib.h>

void run_calc();
void scandata(char *op, double * operand);
void do_next_op(char op, double operand, double *akku);

int main()
{
run_calc();
return 0;
}

void run_calc(){
 double akku = 0, operand = 0;
char op, answer;
printf("Press enter to use the calculator");
printf("\n");
scanf("%c", &answer);

while(answer='q'||answer!='Q');
{
     if(answer=='q'||answer=='Q')
        {
            printf("The last result was %1.2f\n", akku);
            exit(0);
        }

        else if (answer=='h'||answer=='H')
        {
    printf("%s\t%s\n", "+" , "add");
    printf("%s\t%s\n", "-" , "subtract");
    printf("%s\t%s\n", "*" , "multiply");
    printf("%s\t%s\n", "/" , "divide");
    printf("%s\t%s\n", "^" , "power");
    printf("%s\t%s\n", "q" , "quit");
        }
        else
        {
printf("Enter an operator (+,-,/,#,^,*) and optional operand.Enter 'h' for help. Enter 'q' to exit the program.");
scandata(&op, &operand);
do_next_op(op, operand, &akku);
printf("Result so far is: %1.2lf \n", akku);
printf("\n");

        }
}
}



void scandata(char *op, double *operand) {
scanf("%c", op);
 scanf ("%lf", operand);
}

void do_next_op(char op, double operand, double *akku)
{
    switch(op)
    {

    case '+': *akku += operand; break;
    case '-': *akku -= operand; break;
    case '*': *akku *= operand; break;
    case '/': *akku /= operand; break;
    case '#': *akku = sqrt(*akku); break;
    case '^': *akku = pow(*akku,operand); break;
    case '%': *akku *=  -1; break;
    case '!': *akku =  1 / *akku; break;
    case '@': *akku = log(*akku); break;
    case 'q': printf(" The final value of akku is %1.2lf \n", *akku);  exit(0);
}
}

After i run the program and press enter or any letter. it just stucks . can someone help me please? This program is a calculator that i try to do it. This is for my homework which is due to next week. I am still new this programming. i need help and alot of improvement. Can someone point it out what i did wrong?

I think there is something wrong in run_Calc but i dont know what is wrong with it

`answer='q'` Is obviously a typo. But I'm not sure what you really mean that to be because that whole condition looks odd. What exactly do you intend the loop termination condition to be? — kaylum, Oct 17 '20 at 04:56
Does this answer your question? [Why non-equality check of one variable against many values always returns true?](https://stackoverflow.com/questions/26337003/why-non-equality-check-of-one-variable-against-many-values-always-returns-true) — Sotirios Delimanolis, Oct 30 '21 at 21:30

paxdiablo · Answer 1 · 2020-10-17T05:07:29.013

while(answer='q'||answer!='Q');
{

This is an infinite loop. For a start, the semi-colon at the end of the first line disassociates the opening brace^(a) with the while statement meaning that, if the condition is true, it will simply do nothing, forever.

And the condition is true, since answer='q' will set the answer variable to 'q' and then use that as an expression. Since 'q' is non-zero, it's considered true.

However, even if you correct this by changing the = to a != (assuming you only want to continue until user enters quit), you should use && rather than ||. No character can be both q and Q at the same time so using || would also result in the condition always being true.

I suspect what you should have had would be more along the lines of (comparison rather than assignment, get rid of the semicolon, and fix the conjunctive):

while(answer != 'q' && answer != 'Q')
{

There may well be other issues but that's the one causing your apparent "stuck" behaviour.

^(a) A "naked" braced section can be used to create a new, isolated scope, such as:

{
    int xyzzy = 42;
    // Can use xyzzy here.
}
// But not here.

That's what your semicolon is doing in the code you posted.

My calculator stucks after i press enter or any letters. Why?

1 Answers1