Program Displays menu twice after making a selection

This is a discussion on Program Displays menu twice after making a selection within the C Programming forums, part of the General Programming Boards category; I am working on a "Complex Arithmeatic" assignment for a programming class. I have everything working except for one minor ...

  1. #1
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    Angry Program Displays menu twice after making a selection

    I am working on a "Complex Arithmeatic" assignment for a programming class. I have everything working except for one minor issue. The first run through the program the menu displays and I make a selection and enter my numbers and the program returns the answer. However, after this the menu displays twice in a row before allowing me to make another selection. I cannot figure out why this is happening. Any suggestions would be highly appreciated! I have two .c files which I will paste below. The menu is at the end of the second .c file.

    MAIN.C
    Code:
    /*
    Jacob L. Jones
    Computer Programming II
    Lab #5
    */
    
    #include <stdio.h>
    #include "boolean.h"
    #include "complex.h"
    
    
    int main(void) {
    
      complex num1;
      complex num2;
      complex ans;
      char choice;
      boolean quit = 0;
      boolean show_menu = 1;
    
    while (quit == 0){
    
      if(show_menu == 1){
        menu();
        scanf("%c", &choice);
      }
      else{
        printf("Enter your selection: ");
        scanf("%c", &choice);
      }
     
    
       switch (choice){
           case '+':
                 num1 = Read_Complex();
                 num2 = Read_Complex();
                 ans = Add_Complex(num1, num2);
                 Write_Complex(ans);
           break;
    
           case '-':
                num1 = Read_Complex();
                 num2 = Read_Complex();
                 ans = Subtract_Complex(num1, num2);
                 Write_Complex(ans);
           break;
    
           case 'x':
           case 'X':
                 num1 = Read_Complex();
                 num2 = Read_Complex();
                 ans = Multiply_Complex(num1, num2);
                 Write_Complex(ans);
           break;
    
           case '/':
                 num1 = Read_Complex();
                 num2 = Read_Complex();
               if(num2.real == 0 && num2.img == 0){
                 printf("ERROR! Division by zero\n");
               }
                 else{
                 Divide_Complex(num1, num2);
                 }
           break;
    
           case 'c':
           case 'C':
                 num1 = Read_Complex();
                 ans = Conjugate_Complex(num1);
                 Write_Complex(ans);
           break;
    
           case '~':
                 num1 = Read_Complex();
                 ans = Negate_Complex(num1);
                 Write_Complex(ans);
           break;
    
           case 'a':
           case 'A':
                 num1 = Read_Complex();
                 Absolute_Complex(num1);
           break;
    
           case 'm':
           case 'M':
           if(show_menu == TRUE){
             show_menu = FALSE;
             }
           else{
             show_menu = TRUE;
           }
           break;
    
       case 'q':
       case 'Q':
         if(quit == 0){
           quit = 1;
         }
         break;
       }     
     }
    
    }


    COMPLEX.C
    Code:
    #include <stdio.h>
    #include <math.h>
    #include "complex.h"
    
    complex Read_Complex(void){
      complex num;
      printf("Enter real part:");
      scanf("%d", &num.real);
      printf("Enter imaginary part: ");
      scanf("%d", &num.img);
      return num;
    }
    
    void Write_Complex(complex num){
      if(num.img < 0){
        num.img = -1 * num.img;
        printf("The answer is %d - %di\n", num.real, num.img);
      }
      else{
        printf("The answer is %d + %di\n", num.real, num.img);
      }
    }
    complex Add_Complex (complex X1, complex X2){
      complex answer;
    
      answer.real = X1.real + X2.real;
      answer.img = X1.img + X2.img;
      return answer;
    }
    
    complex Subtract_Complex (complex X1, complex X2){
      complex answer;
    
      answer.real = X1.real - X2.real;
      answer.img = X1.img - X2.img;
      return answer;
    }
    
    complex Multiply_Complex (complex X1, complex X2){
      complex answer;
    
      answer.real = X1.real * X2.real - X1.img * X2.img;
      answer.img = X1.real * X2.img + X2.real * X1.img;
      return answer;
    }
    
    complex Negate_Complex (complex num){
      complex answer;
    
      answer.real = -1 * num.real;
      answer.img = -1 * num.img;
      return answer;
    }
    
    complex Conjugate_Complex (complex num){
      complex answer;
    
      answer.real = num.real;
      answer.img = -1 * num.img;
      return answer;
    }
    
    void Absolute_Complex (complex num){
      double answer;
    
      answer = sqrt(num.real * num.real + num.img * num.img);
      printf("The answer is %f\n", answer);
    }
    
    void Divide_Complex (complex X1, complex X2){
      complex answer;
      int den;
      float ar, ai;
     
      answer.real = X1.real * X2.real + X1.img * X2.img;
      answer.img = X1.img * X2.real - X1.real * X2.img;
      den = X2.real * X2.real + X2.img * X2.img;
      ar = answer.real / (float)den;
      ai = answer.img / (float)den;
      printf("The answer is %f + %fi\n", ar, ai);
    }
    
    void menu(){
      printf("+ Add\n");
      printf("- Subtract\n");
      printf("X Multiply\n");
      printf("/ Divide\n");
      printf("C Conjugate\n");
      printf("~ Negate\n");
      printf("A Absolute Value\n");
      printf("M Toggle Menu\n");
      printf("Q Quit\n");
      printf("Enter Selection: ");
    }

  2. #2
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    Long Beach, CA
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    You press enter after you make your choice. scanf("%c", ...) reads just one character, and leaves the enter in the input buffer. The next time through your loop, scanf reads in the enter from the previous time. It doesn't match anything in your case statement, nothing happens and you're back to the top of the loop, printing your menu again. Quick fix: scanf(" %c", ...). That space before the %c ignores leading whitespace, including leftover new lines. Also, read up on flushing the input buffer: FAQ > Flush the input buffer - Cprogramming.com.

  3. #3
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    That was it!! Thank you so much!

  4. #4
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    Douala, Cameroon
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    @jacobj86 i think you can try this at the selection menu while loop........
    while( menu == 1){menu();d = getch(stdin());


  5. #5
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    @Nyah Check:

    That is not a good solution for two reasons. First, getch is not a standard C function, so jacobj86 might not even have it available to him. The standard alternative is getchar. Second, getchar will also leave new lines in the input buffer just like scanf did.

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