Input 50 characters into a string in C

Question

#include<stdio.h>

#include<ctype.h>

#include<string.h>

#define _CRT_SECURE_NO_WARNINGS

int main(void){

//declare 3 char arrays to hold 3 strings of 20 characters each.
char string1[51];
char string2[51];
char string3[51];


// Prompt the user to enter string 1.
printf("Input String 1 : ");

/* Use the gets() function to input the string user enters into string1*/
fgets(string1, sizeof(string1), stdin);

// Prompt the user to enter string 2.
printf("Input String 2 : ");

/* Use the gets() function to input the string user enters into string2*/
fgets(string2, sizeof(string2), stdin);

//Perform the strcpy() operation on string3 from string 1.
//char *strcpy(char *string3, const char *string1);
//strcpy_s(string3, string1, sizeof(string3) - 1);
 memcpy(string3, string1, 51); 


//print string 3
 printf("String3: ");
 printf("%s",string3);

//Use the strlen() function on string 2
 int len;
 len = strlen(string2);

//print the output.
 printf("String 2 length: ");
 printf("%d \n",len);

//Use the strcmp function to compare string and string 2.
 int results;
 strcmp(string1, string2);
 results = strcmp(string1, string2);

 //print the result

if (results < 0) {
    printf("str1 is less than str2\n");
}
else if (results > 0) {
    printf("str2 is less than str1\n");
}
else {
    printf("str1 is equal to str2\n");
}


//Convert characters in string 1 to uppercase using the toupper()  

 
 int i = 0;
 int j = 0;

char chr;
for (i = 0; string1[i]; i++)
{
    chr = string1[i];
    printf("%c", toupper(chr));
}




/*Convert all the characters in string 2 to uppercase using the tolower()  
function on every character using a for loop.*/

 for (j = 0; string2[i]; j++)
 {
    chr = string2[i];
    printf("%c", tolower(chr));
}

return 0;
}

I am trying to copy string1 to string3, but when I use strcpy() or strcpy_s() it throws an error. If I completely remove strcpy() from the program it will run.

I am inputting 50 characters for each string, so do they need to be 51 because of the null?

I have updated my code. I cannot get tolower() to display string2 in lowercase when input uppercase letters.

Please advise me on changes and why they need to be made.

The error: Error C4996 'strcpy': This function or variable may be unsafe.
Consider using strcpy_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS

Answer 1

That error is due to Visual Studio not liking strcpy and suggesting to use strcpy_s, which prevents buffer overruns.

strcpy_s(string3, sizeof(string3), string1);

Please keep in mind that strcpy_s is only available in a few platforms. strncpy is a more portable function that does a similar thing, however you will need to pass it sizeof(string3) - 1 instead of sizeof(string3) and it will not null-terminate the result if all of the 50 bytes of string3 are written, so you will have to do that yourself.

strncpy(string3, string1, sizeof(string3) - 1);
string3[sizeof(string3) - 1] = '\0';

Alternatively, you can #define _CRT_SECURE_NO_WARNINGS and keep using strcpy.