In the function Scanner, the parameters are passed by value. This means that the function Scanner will get its own copy of these variables, and changing the values of these copies will not change the values of the original variables in the function main.
If you want the function Scanner to be able to change the values of the original variables in the function main, then you should not pass the values of the original variables, but you should instead pass pointers that point to the original variables in the function main. That way, the function Scanner can use the pointers to write directly to the original variables.
I suggest that you change the function Scanner to the following:
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
scanf( "%d", p_row1 );
printf( "Write numbers of columns for first matrix: " );
scanf( "%d", p_col1 );
printf( "Write numbers of rows for second matrix: " );
scanf( "%d", p_row2 );
printf( "Write numbers of columns for second matrix: " );
scanf( "%d", p_col2 );
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
The prefix p_ that I added to the variable names just stands for "pointer", but you don't have to use that prefix. You can give them any name that you want.
You can call the function Scanner from the function main like this:
Scanner( &row1, &col1, &row2, &col2 );
Also, since you are dealing with user input, it would probably be better to always check the return value of scanf, in order to determine whether the function succeeded. Otherwise, if the user enters something that is not a number, the conversion will fail, but your program will still attempt to process the non-existant converted value.
Therefore, it would probably be better to write the function like this:
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
printf( "Write numbers of rows for first matrix: " );
if ( scanf( "%d", p_row1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for first matrix: " );
if ( scanf( "%d", p_col1 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of rows for second matrix: " );
if ( scanf( "%d", p_row2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
printf( "Write numbers of columns for second matrix: " );
if ( scanf( "%d", p_col2 ) != 1 )
{
printf( "Input error!\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
However, this solution still does not perform very good input validation yet. For example, if the user enters the number 6abc, then scanf will accept this input as valid input for the number 6. If you do not want this, then you may want to use the function get_int_from_user from this answer of mine to another question. That function will perform very strict input validation, and it will automatically reprompt the user for input if the input is not a number.
If you do decide to use my function get_int_from_user, then you could write the function like this:
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied.\n" );
exit( EXIT_FAILURE );
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n" );
exit( EXIT_FAILURE );
}
}
However, the user is now automatically reprompted by the function get_int_from_user when the input is not a number, but the user won't get reprompted at all when the input is invalid for another reason. To fix this inconsistency, the function could be written like this:
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
This program could be improved further by restarting the input as soon as the user enters one non-positive number, instead of waiting until the user has entered all 4 numbers. However, I don't want to make my answer to complicated.
Here is a small demonstration program of the latest version of the function Scanner:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <errno.h>
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 );
int get_int_from_user( const char *prompt );
int main( void )
{
int row1, col1, row2, col2;
Scanner( &row1, &col1, &row2, &col2 );
printf(
"\n"
"The variables in the function main now have the\n"
"following values:\n"
"\n"
"row1: %d\n"
"col1: %d\n"
"row2: %d\n"
"col2: %d\n",
row1, col1, row2, col2
);
}
void Scanner( int *p_row1, int *p_col1, int *p_row2, int *p_col2 )
{
//loop forever until input is valid
for (;;) //infinite loop, equivalent to while(1)
{
*p_row1 = get_int_from_user(
"Write numbers of rows for first matrix: "
);
*p_col1 = get_int_from_user(
"Write numbers of columns for first matrix: "
);
*p_row2 = get_int_from_user(
"Write numbers of rows for second matrix: "
);
*p_col2 = get_int_from_user(
"Write numbers of columns for second matrix: "
);
if( *p_col1 != *p_row2 )
{
printf( "Matrixes can't be multiplied. Try again!\n\n" );
continue;
}
if( *p_col1 <= 0 || *p_row1 <= 0 || *p_col2 <= 0 || *p_row2 <= 0 )
{
printf( "Numbers have to be positive.\n\n" );
continue;
}
//input is valid, so we can break out of the infinite loop
break;
}
}
int get_int_from_user( const char *prompt )
{
for (;;) //loop forever until user enters a valid number
{
char buffer[1024], *p;
long l;
//prompt user for input
fputs( prompt, stdout );
//get one line of input from input stream
if ( fgets( buffer, sizeof buffer, stdin ) == NULL )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
//make sure that entire line was read in (i.e. that
//the buffer was not too small)
if ( strchr( buffer, '\n' ) == NULL && !feof( stdin ) )
{
int c;
printf( "line input was too long!\n" );
//discard remainder of line
do
{
c = getchar();
if ( c == EOF )
{
fprintf( stderr, "unrecoverable error reading from input!\n" );
exit( EXIT_FAILURE );
}
} while ( c != '\n' );
continue;
}
//attempt to convert string to number
errno = 0;
l = strtol( buffer, &p, 10 );
if ( p == buffer )
{
printf( "error converting string to number!\n" );
continue;
}
//make sure that number is representable as an "int"
if ( errno == ERANGE || l < INT_MIN || l > INT_MAX )
{
printf( "number out of range error!\n" );
continue;
}
//make sure that remainder of line contains only whitespace,
//so that input such as "6sdfj23jlj" gets rejected
for ( ; *p != '\0'; p++ )
{
if ( !isspace( (unsigned char)*p ) )
{
printf( "unexpected input encountered!\n" );
//cannot use `continue` here, because that would go to
//the next iteration of the innermost loop, but we
//want to go to the next iteration of the outer loop
goto continue_outer_loop;
}
}
return l;
continue_outer_loop:
continue;
}
}
This program has the following behavior
Write numbers of rows for first matrix: abc
error converting string to number!
Write numbers of rows for first matrix: 6abc
unexpected input encountered!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 8
Write numbers of columns for second matrix: 9
Matrixes can't be multiplied. Try again!
Write numbers of rows for first matrix: 6
Write numbers of columns for first matrix: 7
Write numbers of rows for second matrix: 7
Write numbers of columns for second matrix: 8
The variables in the function main now have the
following values:
row1: 6
col1: 7
row2: 7
col2: 8
