How can fix this value bug?-CodePudding

I have problem about wrong values. How can i control input data. If user enter char value , my code is give error. I'm beginner coder so i couldn't fix it. Waiting for your advice.(I'm sharing some of it because my code doesn't fit)

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

#define PI 3.14 // We define pi number with this code.

int main() {
    printf(" Welcome to the geometric shapes calculator. \n (Press the number you want to operate from 1 to 9.) ");
    char lastChoice[30];

    do {
        printf("\n Please choose the geometric shapes you want to calculate");
        printf("\n GEOMETRIC SHAPES \n 1-Square \n 2-Triangle \n 3-Rectangle \n 4-Parallelogram \n 5-Rhombus \n 6-Circle \n 7-Trapezoid \n");
        int choice1;
        scanf("%d", &choice1);
        if (choice1 > 7 || choice1 < 1) {
            printf("\n You chose wrong operate.");
            printf("\n Do you want to do calculation ? \n (Please press y if you want to continue to calculation)");
            scanf("%s", &lastChoice);
        }

        if (choice1 == 1) {
            printf("Please choose the measurement you want to calculate. \n ");
            printf("\n 1-Perimeter \n 2-Area \n 3-Volume \n 4-All of them \n");
            int choice2;
            scanf("%d", &choice2);
            if (choice2 == 1) {
                printf("Please write the length of edge. \n");
                float squareEdge;
                scanf("%f", &squareEdge);
                printf("Perimeter of the square : %.2f", 4 * squareEdge);
            }
            if (choice2 == 2) {
                printf("Please write the length of edge. \n");
                float squareEdge;
                scanf("%f", &squareEdge);
                printf("Area of the square : %.2f", squareEdge * squareEdge);
            }
            if (choice2 == 3) {
                printf("2D geometric shapes have not volume. \n");
                printf("\n Do you want to do calculation ? \n (Please press y if you want to continue to calculation.)");
                scanf("%s", lastChoice);
              }
       }
     }while (strcmp(lastChoice, "y")==0);
}

CodePudding user response：

Pay attention to your compiler warnings.

main.c:19:21: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘char (*)[30]’ [-Wformat=]
   19 |             scanf("%s", &lastChoice);
      |                    ~^   ~~~~~~~~~~~
      |                     |   |
      |                     |   char (*)[30]
      |                     char *

Name of the array is already a pointer to the first element, you shouldn't be taking the address of it.

scanf( "%s", lastChoice );

Also, scanf is not the tool for taking user input. Please seek alternatives. see

CodePudding user response：

How can i control input data. If user enter char value ,

Although a bit much for a beginner, consider using helper functions to get user input and avoid scanf() everywhere.

Read using fgets() and then parse the input string.

Example for reading a limited range int.

#include <ctype.h>
#include <strlib.h>

// Return 0 on success
// EOF on end-of-file
// 1 on unrecoverable error
int read_int(int *result, int min, int max) {
  char buf[100];
  while (fgets(buf, sizeof buf, stdin)) {
    char *endptr;
    errno = 0;
    long val = strtol(buf, &endptr, 10); 
    unsigned char *end = endptr;
    while (isspace(*end)) end  ; 
    // If conversion, no overflow, no junk at end of string, in range
    if (endptr > buf && errno == 0 && *end == '\0' && val >= min && val <= max) {
      *result = (int) val;
      return 0; // no error
    }
    printf("\n You chose invalid `int`.\n"); 
    printf("Do you want to do calculation ? \n"
    printf(" (Please press y if you want to continue to calculation)\n");
    TBD code and then return 1 or continue;
  }
  return EOF;
}

Likewise for other inputs like read_float(), etc.

Or check scanf() return value:

    for (;;) {
      int count = scanf("%d", &choice1);
      if (count == EOF) {
        return EXIT_FAILURE;  // stdin is closed
      } 
      if (count == 1 && choice1 >= 1 && choice1 <= 7) {
        break; // Success!
      }

      // Get rest of line in some fashion including that non-numeric input.
      int ch;
      while ((ch = gethar()) != '\n' && ch &= EOF) {
        ;
      }

      printf("\nYou chose wrong operate.\n");
      printf(" Do you want to do calculation ? \n");
      printf(" (Please press y if you want to continue to calculation)");

      unsigned char lastChoice[30];
      count = fgets(lastChoice, sizeof lastChoice, stdin);
      if (count == NULL || toupper(lastChoice) != 'Y')  {
        return EXIT_FAILURE;
      }
    }

Even with this approach, I recommend a helper function.

User input is evil. Do not trust it until well vetted.