int main(void)
{
 int c, countSpaces = 0;

printf("Type sentence:n");

do
{
  c = getchar();
  if (c == ' ')
    countSpaces = countSpaces + 1;
}
while (c != 'n');

printf("Sentence contains %d Spaces.n", countSpaces);

return 0;
}

if (c != EOF)
    countSpaces = countSpaces + 1;
}
while (c != 'n');

printf("Sentence contains %d Spaces.n", countSpaces - 1);

#include <stdio.h>

int main(void)
{
    int c;
    int countSpaces = 0;
    int countChars = 0;

    puts("Type sentence:");

    do {
        c = getchar();
        countChars += 1;
        if (c == ' ') {
            countSpaces += 1;
        }
    } while (c != 'n');

    printf("Sentence contains %d spaces and %d characters.n", countSpaces, countChars);

    return 0;
}

if( condition )
    do something
    whoops this is not in the condition but it sure looks like it is!

$ ./test
Type sentence:
foo bar baz
Sentence contains 2 spaces and 12 characters.

// Note, the parenthesis around `c = getchar()` are important.
while( (c = getchar()) != 'n' ) {
    countChars++;
    if (c == ' ') {
        countSpaces++;
    }
}

$ ./test
Type sentence:
foo bar baz
Sentence contains 2 spaces and 11 characters.

#include <stdio.h>

int main()
{
    char *str = calloc(sizeof(char),50);
    int i = 0, count = 0;

    printf("Type sentence:n");
    scanf("%s",str);

    while (str[i++] != '')
        count++;                    //length of the string

    printf("%d",count);
    return 0;
}

#include <stdio.h>

int main(void)
{
    int i;
    int length = 0;
    char buffer[1024];

    printf( "Enter some text> " );
    fgets( buffer, sizeof(buffer), stdin );

    // If the user inputs > 1024 letters, buffer will not be n terminated
    for ( i=0; buffer[i] != 'n' && buffer[i] != ''; i++ )
    {
        length += 1;
    }

    printf( "length: %dn", length );

    return 0;
}