patterncMinor

Happy Birthday Program

Submitted by: @import:stackexchange-codereview·Mar 10, 2026·

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birthdayprogramhappy

Problem

I'm trying to teach myself C. I've managed to make this program I call HappyToYou.c (inspired by this video):

#include 
//#include  //malloc would need this.
#include 
#include 

void sing(char *start, char *end){
    printf("%s%s.\n", start, end);
}

int main(int argc, char *argv[]){
    if(argc!=3) errx(1, "Give a holiday and a name as arguments.");

    char *happy="Happy ";
    char start[strlen(happy)+strlen(argv[1])+1];
    strcpy(start, happy);
    strcat(start, argv[1]);
    char *to=" to you";

    char *dear=" dear, ";
    char person[strlen(dear)+strlen(argv[2])+1];
    strcpy(person, dear);
    strcat(person, argv[2]);

    sing(start, to);
    sing(start, to);
    sing(start, person);
    sing(start, to);

    return 0;
}

I think it is free from bugs (as far as I know). I'm pretty sure it can be trimmed down but I'm not sure how.

Solution

There're some bugs in the code. For example, if the user provides more inputs than needed, which the program could safely ignore (or warn about), it'll still exit with an error and an incorrect message.

The comparison should be updated to: if (argc Some inputs appear to be missing. Please enter the holiday and your name.
Usage: HappyToYou
Example: HappyToYou Birthday Bob
`

Few things are more frustrating than error messages that are uninformative or wrong because the former doesn't help you resolve the issue and the latter sends the user down the wrong path in trying to find a solution.

Code Snippets

#include <stdio.h>
#include <error.h>

int main(int argc, char *argv[]) {
    /* notice the logical operator update here; prevents bogus error
       message if user provides more than 2 inputs */
    if (argc < 3)
        errx(1, "Give a holiday and a name as arguments.");

    printf(
        "Happy %1$s to you.\n"
        "Happy %1$s to you.\n"
        "Happy %1$s, dear %2$s!\n"
        "Happy %1$s to you.\n",
        argv[1],
        argv[2]
    );

    return 0;
}

Context

StackExchange Code Review Q#106487, answer score: 6

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