Print the month corresponding to appropriate input

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 开发者_运维百科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;
        }
}

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.

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;
}

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.

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.

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.

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.