Strange problem with input in a C programm with Strings.

Hello to all.... I have a problem in my code. Well I have done a program (an exercise) that it takes your name (first + last) for instance you may have something like :

Code:

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Enter your name: Bill Gates

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And the program will produce the following output :

Code:

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  Gates , B.

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The code is :

Code:

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#include <stdio.h>
#include <string.h>  // strcat()
#include <ctype.h>
#define STR_LEN 80
void reverse_name(char *);
void read_line( char * , int );
 
int main(void)
{
    char name[STR_LEN+1] = {'\0'};
   
    printf("Enter your name: ");
    read_line(name , STR_LEN);
    puts(name);
    reverse_name(name);
    puts(name);
   
    return 0;
}
void read_line(char name[] , int n)
{
    int ch , i=0;
   
    while( (ch = getchar()) != '\n' ) {
       
        if(i < n )
        name[i++] = ch;
    }
       
        name[i] = '\0';
}

void reverse_name(char *name)
{
    char *p = name, first_letter[1+1];
   
    while (*p == ' ') p++; // Skip blanks in the beginning
    first_letter[0] = *p;  // save the 1st character of the first name
   
    while (*p != ' ') p++; //
    while (*p == ' ') p++; // skip blanks between first and last name
   
    for (; *p != ' ' && *p; p++, name++)
        *name = *p;    // Copy last name into first name
     
          *name = '\0';
 
   
    strcat(name, ", ");  // Gates,
    strcat(name, first_letter);  // Gates, B
    strcat(name, "."); // Gates, B.

}

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If I don't use the first call of puts function in my main... the result of the program is undefined for example....

Code:

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 printf("Enter your name: ");
    read_line(name , STR_LEN);
    ///puts(name);
    reverse_name(name);
    puts(name);

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Code:

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Gates , B ^ | ? .

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If I use the first call of puts ... the result is regular. Why??????????

I can't understand.... where is the problem ?

puts will print until it finds a null terminator and then will append a newline automatically. I just run your code on windows and on Linux and was ok..

When program execution reaches line 48, what character does "first_name[0]" contain?
What about "first_name[1]"?

Quote:

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Originally Posted by Matticus

When program execution reaches line 48, what character does "first_name[0]" contain?
What about "first_name[1]"?

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The 'B' character. If you assume the example with the output of Bill Gates. Generally it will have the first character of the first name.

And YES that is the solution of the problem. Array first_name has no a null terminator. The call of strcat may has the problem.... I will find it.

p.s The array first_name was uninitialized . That was the problem... With the initialization strcat knows what will append at the end of name string....

the characters 'B' , '\0' .

Gates, B.