C programming, calling a function

Remember that C code is compiled top-to-bottom. The function get_next_line isn't declared by the time the while line is read.

Either move get_next_line's definition to before main's, or forward-declare it by saying:

char *get_next_line(FILE *fpntr);

beforehand. The reason that you're getting a warning instead of an error is that undeclared functions are assumed to return int and no assumptions are made about their parameters. That is, they have the type int().

Also, properly format your code for both your sake and of those who will be answering your questions (or working with you.)

add a * to the pointer of integer to convert it from pointer to integer

... i am trying to iteratively call line in stream...

Why not use fgets()?

Secondly, to match a substring in a string, you can use strstr()

Please use standard C library instead of re-inventing the wheel. It saves the day usually.

#include <assert.h> // I'm too dumb to program without assertions!
#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
//#include <unistd.h>  I prefer stdlib.h, couldn't see any need for non-portable header...

#define MAX_LINE    (101)       // define funky constants in one place for easy changing later.

// declare functions before using them
void grep_stream(FILE *fpntr, char *file_pathname);
char *get_next_line(FILE *fpntr);


int main(int argc, char *argv[]) {

    FILE *fpntr;
    char *file_pathname;

    if (argc != 2) {
        fprintf(stderr, "usage: %s FILE\n", argv[0]);
        return EXIT_FAILURE;
        }
    file_pathname = argv[1];

    if ((fpntr = fopen(file_pathname, "r")) == NULL ) {
        fprintf(stderr, "Error opening file %s: %s\n", file_pathname, strerror(errno));
        return EXIT_FAILURE;
        }
    else {
        grep_stream(fpntr, file_pathname);
        fclose(fpntr);
        }
    return EXIT_SUCCESS;
    }

void grep_stream(FILE *fpntr, char *file_pathname) {
    char*   line;
    int     got_first = 0;

    assert(fpntr);
    assert(file_pathname);  // I worry the guy who wrote main() might be an idiot like me!

    //warning is on next line [not anymore!]
    while ((line = get_next_line(fpntr)) != NULL ) {
        if(!got_first) {
            printf("First line in : %s \n%s\n", file_pathname, line);
            got_first = 1;
            }
        // if we're not going to use it, let's not leak memory
        free(line);
        }
    }


char *get_next_line(FILE *fpntr) {
    char *buff = malloc(MAX_LINE);
    int pos = 0;
    int next;

    assert(buff != NULL);   // wouldn't it be nice to know malloc() worked?
    while ((next = fgetc(fpntr)) != '\n' && next != EOF) {
        buff[pos++] = (char)next;
        assert(pos < (MAX_LINE-1)); // don't want to be right back on SO with a seg fault, eh?
        }
    buff[pos] = '\0';

    if(next == EOF) {
        free(buff);
        buff = NULL;
        }

    return buff;
    }