Print the month corresponding to appropriate input

Question

I have to write a program the takes in two integers by the user, a and b, where a corresponds to the month of the year ( 1 = jan, 2 = feb etc.). The program has to print the month that comes after "a" and the following "b" months. This is what I have so far, but for every two integers I enter, I always get the same output: "January, February". Any help is appreciated.

#include<stdio.h>

        enum month {jan,feb,mar,apr,may,jun,jul,aug,sep,oct,nov,dec}; /*This
allows yoou to name a finite set and to declare identifiers*/
        typedef enum month      month;

month next_month(month M)  /*this is a function definition*/
{
        switch (M) /* like an if-else statement, if this month is true goto the M=month you chose*/
        {
        case  jan:
                M=feb;break;
        case  feb:
                M=mar;break;
        case  mar:
                M=apr;break;
        case apr:
                M=may;break;
        case may:
                M=jun;break;
        case jun:
                M=jul;break;
        case jul:
                M=aug;break;
        case aug:
                M=sep;break;
        case sep:
                M=oct;break;
        case oct:
                M=nov;break;
        case nov:
                M=dec;break;
        case dec:
                M=jan;break;
        }
        return M;
}
void print_month (month M)  /*this is a function definition*/
{
        switch (M)  /* like an if-else statement, if this month is true goto the M=month you chose*/
        {
        case jan:
                printf("January");break;
        case feb:
                printf("February");break;
        case mar:
                printf("March");break;
        case apr:
                printf("April");break;
        case may:
                printf("May");break;
        case jun:
                printf("June");break;
        case jul:
                printf("July");break;
        case aug:
                printf("August");break;
        case sep:
                printf("September");break;
        case oct:
                printf("October");break;
        case nov:
                printf("November");break;
        case dec:
                printf("December");break;
        }
}
int main(void)
{
        month M, N, sat;
        printf("Please enter two integers:\n");
        scanf("%d%d", &M, &N);
        for (M = jan; M <= N; ((int)M++))
        {
                printf(" ");
                print_month(M);  /*function call to print month*/
                printf(" ");
                print_month(next_month(M));  /*function call to print previous month*/
                putchar('\n');
                return;
        }
}

Answer 1

You have this in main

    scanf("%d%d", &M, &N);
    for (M = jan; M <= N; ((int)M++))
    {
         /* ... */
    }

So ... in the scanf line you change M (and N) to the values supplied by the user
and right after that you set M to jan effectively losing what he user chose.

You need to review the way you're doing it.

Answer 2

My suggestion for improving your program is to replace your switch statements with an array of month names. It would be a lot easier to program and to read.

It is usually a great improvement whenever you can replace code with data structures. This is something to remember and use whenever you do programming in the future.

So following my advice to use a month array would look a little bit like this:

#include <stdio.h>

const char* months[12] = {
 "January", "February", "March", "April", "May", "June",
 "July", "August", "September", "October", "November", "December"
};

int main(void)
{
    int m;
    printf("Enter month: ");
    scanf("%d", &m);
    if( 1 <= m && m <= 12 ) {
        printf("%s\n", months[m-1]);
    }
    return 0;
}

Answer 3

return means return from the current function, so in the end of the first iteration of your for loop, you return from main function, and the program exits.

Answer 4

Try this code:

int main(void)
{
        int a, b, m;
        printf("Please enter two integers between 1-12:\n");
        scanf("%d%d", &a, &b);
        for (m=a+1; b; b--, m++)
        {
                printf(" ");
                print_month(m);  /*function call to print month*/
                putchar('\n');
        }
}

Take care, Beco

PS. Edited:

Also, change the enum line to:

    enum month {jan=1,feb,mar,apr,may,jun,jul,aug,sep,oct,nov,dec};

And take care of the possible overflow a+b>12

2nd. Edition: Another explanation might be useful: you cannot use a return inside a loop like this and expect the loop will run, because at the time the computer runs the return it exits the program for good.

Answer 5

include <stdio.h>

const char* months[12] = {
 "January", "February", "March", "April", "May", "June",
 "July", "August", "September", "October", "November", "December"
};

int main(void)
{
    int m;
    printf("Enter month: ");
    scanf("%d", &m);
    if( 1 <= m && m <= 12 ) {
        printf("%s\n", months[m-1]);
    }


    return 0;
}

Worked for me. thank you.

Answer 6

Check out C/C++ documentation of "%" and of macros - "#define". For this problem, Switches are unnecessary, inefficient and make code long.

Increment and modulus can be used to increment month. Enumerated value to sting can be done with a macro that replaces value code with string containing same code.

Enum to string using macros:
MSDN link - Stringizing Operator (#)

There are many ways to use this to convert enums to strings (Google it), including:

// Use correct number of parameters here (can use multiple macros)
#define ENUM_MACRO(name, offset, v1, v2, v3, v3)\
    enum name { v1 = offset, v2, v3, v4};\
    const char name##Strings[] = { #v1, #v2, #v3 };\
    const char* name##ToString(value) { return name##Strings[value - offset]; }

// This way you do not have two different
// lists of months to maintain in your code
// (the preprocessor creates them)
ENUM_MACRO(Month, 1, January, February, March);

//
// usage:
//
Month month = Month::Janurary;
const char* st = MonthToString(month);

//
// Incrementing month taking offset (1) and max (12) into account
//
month = (month + 1) % 12 + Month::Janurary;

Using these methods you can greatly reduce the size of your code, making it easier to read and maintain. Also - you improve performance by getting rid of all the branches.

Disclaimer - I haven't compiled this code, written from memory.