Keep getting gibberish output when trying to print an array in C - c

Question

I am trying to write a program that reverses words in a sentence, the code is able to do that but also prints gibberish in between. (see below code for sample)
#include <stdio.h>
#define MAX_VALUE 50
int main(){
char c[MAX_VALUE],
b[MAX_VALUE];
int i = 0, j = 0;
while ((c[i] = getchar()) != '\n'){
i++;
}
for(i = MAX_VALUE; i >= 0; i--){
if (c[i] == ' '){
for(j = i+1; j < MAX_VALUE; j++){
if (c[j] != ' '){
printf("%c", c[j]);
}
else{
break;
}
}
printf(" ");
}
}
while (c[i] != ' '){
printf("%c", c[i]);
i++;
}
}
Loop goes backwards when it detects a space it prints the word until it finds another space then goes backwards again from where it left off last
The input and output expected:
input: test a is this
output: this is a test
What I get:
input: test a is this
output:
this
`����l�,+�D �=� is a test

Answer 1

This for loop
while ((c[i] = getchar()) != '\n'){
i++;
}
can write outside the array c and store the new line character '\n' in the array.
And this output consisting from two lines
this
`����l�,+�D �=� is a test
demonstrates that the new line character was stored in the array.
Also you forgot to append the entered sequence of characters with the zero terminating character '\0' to form a string.
You could write the while loop the following way
int ch;
while ( i < MAX_VALUE - 1 && ( ch = getchar() ) != '\n' && ch != EOF ){
c[i++] = ch;
}
c[i] = '\0';
Or if you want store the entered sequence without the terminating zero character '\0' then the loop can look like
int ch;
while ( i < MAX_VALUE && ( ch = getchar() ) != '\n' && ch != EOF ){
c[i++] = ch;
}
In this case the variable i will contain the number of entered symbols in the array and you should use its value instead of the value MAX_VALUE in the following loops.
This outer for loop
for(i = MAX_VALUE; i >= 0; i--){
is incorrect because the user can enter a sequence of symbols that contains less than MAX_VALUE symbols. You should either use standard string function strlen (if you appended the sequence with the terminating zero character '\0') to determine the length of the string stored in the array or the value of the variable i as mentioned above that denotes the number of entered symbols.
And it is not enough to check this condition
if (c[i] == ' '){
because the leading spaces can be absent in the entered string. So you need to check also whether i is equal to 0. Otherwise the output can be incorrect if the sequence contains for example only one word.
The inner for loop
for(j = i+1; j < MAX_VALUE; j++){
again is incorrect by the same reason of using MAX_VALUE in the condition.
Pay attention to that the array b
char c[MAX_VALUE],
b[MAX_VALUE];
is not used in your program.
Using your approach I can suggest the following solution to output words of a string in the reverse order shown in the demonstrative program below.
#include <stdio.h>
#include <string.h>
#include <ctype.h>
int main( void )
{
const char *s = "test a is this";
for( size_t i = strlen( s ); i != 0; )
{
while ( i != 0 && isblank( ( unsigned char )s[i-1]) )
{
putchar( s[--i] );
}
size_t j = i;
while ( j != 0 && !isblank( ( unsigned char )s[j-1]) )
{
--j;
}
if ( j != i )
{
size_t last = i;
i = j;
while ( j != last )
{
putchar( s[j++] );
}
}
}
putchar( '\n' );
}
The program output is
this is a test

Answer 2

The code uses two arrays and two 'counters', and fiddles around with individual characters one-at-a-time. It's easy to get lost and use an upper bound that is outside the array size.
Simplify! This "reversal" is an excellent example of when recursion should be the go-to method of solving the problem.
#include <stdio.h>
#include <string.h>
void output( char *p ) {
if( (p = strtok( p, " " )) == NULL ) return;
output( NULL );
printf( "%s ", p );
}
int main() {
char str[] = "The quick brown fox jumps over the dogs";
output( str );
return 0;
}
dogs the over jumps fox brown quick The
Some purists may want an entire buffer to be assembled before printing. This resulting string includes an invisible SP at the end that could be lopped off if desired.
#include <stdio.h>
#include <string.h>
char *revWords( char *dst, char *p ) {
if( (p = strtok( p, " " )) == NULL ) return NULL;
revWords( dst, NULL );
return strcat( strcat( dst, p ), " " );
}
int main() {
char str[] = "The quick brown fox jumps over the dogs";
char buf[sizeof str + 1 + 1] = { 0 }; // important to initialise
puts( revWords( buf, str ) );
return 0;
}
For an alternative, here's a version without recursion. It requires, like above, a mutable buffer holding the string.
#include <stdio.h>
#include <ctype.h>
int main() {
char str[] = " The quick brown fox jumps over the dogs ";
int i = 0;
// note: 1 string buffer, 1 index variable
for( i = 0; str[i]; i++ ) ; // loop
while( i >= 0 ) {
while( i >= 0 && !isalnum( str[ i ] ) ) str[i--] = '\0';
while( i >= 0 && isalnum( str[ i ] ) ) i--;
printf( "%s ", str + i + 1 );
}
puts( "" );
return 0;
}