Code:
#include <stdio.h>

void main(void){
          int lines=0;
          char tmp[256];
          int maxwidthofline = 132;     // put the max line len here
          FILE *in;
          in = fopen("myfile.dat","r");
          while (!feof(in) ) {
               if (fgets(tmp,maxwidthofline,in) != NULL ) lines++;
          }
          fclose(in);
          printf("%d\n",lines);

}