Write a program that reads a short string and a longer string and checks if the longer string starts with the letters of the short string. Use strncmp

Question

I need help getting this code to work. Could someone tell me how to properly use strncmp and how to get this to work?

Example: Enter first string: john
Enter second string: johnson
johnson does start with john

This is my code here:

#include <stdio.h>  
#include<string.h>  
int main()  
{  
   char str1[20];   
   char str2[20];    
   int value;   
   printf("Enter the first string right here: ");  
   scanf("%s",str1);  
   printf("Enter the second string right here: ");  
   scanf("%s",str2);  
    
   value=strncmp(str1,str2);  
   if(value==0)  
   printf("Your strings are the same");  
   else  
   printf("Your strings are not same");
  
   return 0;  
  }

This is what my error code is below

main.c:13:27: error: too few arguments to function call, expected 3, have 2
   value=strncmp(str1,str2);  
         ~~~~~~~          ^
1 error generated.
make: *** [<builtin>: main.o] Error 1
exit status 2 ```

Did you read the error message? It is telling you that strncmp needs 3 arguments. Read the documentation of strncmp, and don't confuse it with strcmp. — David Grayson, Apr 15 '22 at 14:33
`int strncmp(const char *s1, const char *s2, size_t n);` : compares only the first (at most) n bytes of s1 and s2. — जलजनक, Apr 15 '22 at 14:34
Also note that I can easily break your program, by entering a string longer than 19 characters. You need to protect yourself against that, for example by imposing a limit in your `scanf` format strings, like `"%19s"`. — Some programmer dude, Apr 15 '22 at 14:38

Vlad from Moscow · Accepted Answer · 2022-04-15T14:41:54.853

Before calling the function strncmp

value=strncmp(str1,str2);

you should check that str1 is indeed is not less than str2 or vice versa because in your program it is unclear where the user entered a more shorter string and where he entered a more larger string.

But in any case the function strncmp expects three arguments.

At least you have to write

value=strncmp(str1,str2, strlen( str2 ));

The function is declared like

int strncmp(const char *s1, const char *s2, size_t n);

You could write for example

size_t n1 = strlen( str1 );
size_t n2 = strlen( str2 );

value = strncmp( str1, str2,  n2 < n1 ? n2 : n1 );

Also the text in the calls of printf does not satisfy the assignment

printf("Your strings are the same"); 
printf("Your strings are not same");

You are not determining whether two strings are equal. You need to determine whether one string contains another string in its beginning.

Write a program that reads a short string and a longer string and checks if the longer string starts with the letters of the short string. Use strncmp

1 Answers1