Keyword detection

#include<stdio.h>
#include<string.h>
int main()
{

    char str[1000],ab[1000];
    printf("Enter a string: ");
    scanf("%[^\n]%*c",str);
    int i,p,q=0;

    for(i=0; str[i]!='\0' ; i++)
    {
        if(str[i]=='f')
        {
            p=i;
            if(str[p+1]=='o' && str[p+2]=='r' && str[p+3]==' ' )
            {
                ab[q]=str[i];
                q++;
                ab[q]=str[p+1];
                q++;
                ab[q]=str[p+2];
                q++;
                ab[q]=' ';
                q++;
            }

        }
        else if(str[i]=='w')
        {
            p=i;
            if(str[p+1]=='h' && str[p+2]=='i' && str[p+3]=='l' && str[p+4]=='e' && str[p+5]==' ')
            {
                ab[q]=str[i];
                q++;
                ab[q]=str[p+1];
                q++;
                ab[q]=str[p+2];
                q++;
                ab[q]=str[p+3];
                q++;
                ab[q]=str[p+4];
                q++;
                ab[q]=' ';
                q++;
            }
        }

    }
    ab[q]='\0';

    printf("\nKeywords are: ");
    for(i=0; ab[i]!='\0'; i++)
    {
        printf("%c",ab[i]);
    }
}