Format specifier %s in not showing result-CodePudding

I am learning the C programming language. I am doing homework with C programming language. But I am getting a problem. The result is not printing. I am using format specifier %s. Here is my code below. Please have a look.

#include <stdio.h>

int gradeCalculation(int marks) {
  switch (marks) {
    case 0 ... 49:
      return 'F';
      break;
    
    case 50 ... 59:
      return 'D';
      break;

    case 60 ... 69:
      return 'C';
      break;

    case 70 ... 79:
      return 'B';
      break;

    case 80 ... 89:
      return 'A';
      break;

    case 90 ... 100:
      return 'A ';
      break;

    default:
      return 'Marks is not valid!';
  }
}

int main() {
  int marks;

  printf("Marks: ");
  scanf("%d", &marks);

  printf("Grade: %s\n", gradeCalculation(marks));

  return 0;
}

How to solve my problem? What specifier should I use to get the expected result?

CodePudding user response：

Apostrophes denote character constants; F is an integer that is the code for the character “F”.

For various legacy/history reasons, you can have multi-character constants such as A , which has a value that may combine the values of the two characters “A” and “ ”. However, the result is still an int; it is not generally treated as a string of two characters. Multi-character constants are used for special purposes and are implementation-dependent. You should avoid them outside of special circumstances.

In gradeCalculation, you want to return a string of characters. To refer to a string, we generally use a pointer to its first element. So make the return type of gradeCalculation const char *. Then change all the character constants to string literals, such as "F", "A ", and "Marks is not valid". Note the use of quotation marks rather than apostrophes. A string literal denotes an array of characters including a null character to mark the end.

CodePudding user response：

For starters case labels like this

case 90 ... 100:

is not a standard C feature. It is better to use if-else statements. Also the function parameter should have unsigned integer type for example unsigned int.

Your function returns an object of the type int

int gradeCalculation(int marks) {

So using the conversion specifier %s with an object of the type int results in undefined behavior.

The function return type should be const char *

const char * gradeCalculation( unsigned int marks ) {

and instead of integer character literals you need to return string literals as for example

case 80 ... 89:
  return "A";
  break;

case 90 ... 100:
  return "A ";
  break;

default:
  return "Marks is not valid!";

Your program can look the following way

#include <stdio.h>

const char * gradeCalculation( unsigned int marks ) 
{
    const char *grade = "Marks is not valid!";

    if ( marks < 50 )
    {
        grade = "F";
    }
    else if ( marks < 60 )
    {
        grade = "D";
    }
    else if ( marks < 70 )
    {
        grade = "C";
    }
    else if ( marks < 80 )
    {
        grade = "B";
    }
    else if ( marks < 90 )
    {
        grade = "A";
    }
    else if ( marks <= 100 )
    {
        grade = "A ";
    }

    return grade;
}

int main( void ) 
{
    unsigned int marks = 0;

    printf("Marks: ");
    scanf( "%u", &marks );

    printf( "Grade: %s\n", gradeCalculation( marks ) );

    return 0;
}

CodePudding user response：

There are few points to be noted in your given code:

In the line printf("Grade: %s\n", gradeCalculation(marks)); , the function gradeCalculation() returns an int whereas the format specifier is %s which is for a string(char *).
In the int gradeCalculation(int marks), all the cases are returning a character, except for

case 90 ... 100:

return 'A ';

break;

default:

return 'Marks is not valid!';

which are returning string.

Therefore, it will be good to convert all to string and change the return type to char *, i.e., string.

Below is the solution :-

#include <stdio.h>

char * gradeCalculation(int marks) {
  switch (marks) {
    case 0 ... 49:
      return "F";
      break;
    
    case 50 ... 59:
      return "D";
      break;

    case 60 ... 69:
      return "C";
      break;

    case 70 ... 79:
      return "B";
      break;

    case 80 ... 89:
      return "A";
      break;

    case 90 ... 100:
      return "A ";
      break;

    default:
      return "Marks is not valid!";
  }
}

int main() {
  int marks;

  printf("Marks: ");
  scanf("%d", &marks);

  printf("Grade: %s\n", gradeCalculation(marks));

  return 0;
}