Guide for The C Programming Language Chapter 4

Transcription

1 1. What is Structure? Explain the syntax of Structure declaration and initialization with example. A structure is a collection of one or more variables, possibly of different types, grouped together under a single name for convenient handling. Syntax of structure declaration: struct struct_tag type_1 var_1; type_2 var_2; type_n var_n; structvar1, structvar2; The word struct is the keyword in C. struct_tag identifies the structure in the program. type_1, type_2,,type_n can be any data type in C including another structure. var_1, var_2,.,var_n are the member of the structure. structvar1, strubtvar2 are variables which have the format of struct_tag. Example of declaration and initialization of structure: struct student char idno[12]; char name[40]; float average; std1= 45BN21CS6052, John Abraham,76.82; 2. Write a C program to maintain a record of n employee detail using an array of structures with three fields (id, name, salary) and print the details of employees whose salary is above #include<stdio.h> #include<string.h> struct employee char id[10]; char name[20]; int salary; ; int main() int i,n; struct employee s[100]; printf( \n Enter the number of employees(maximum=100): ); scanf( %d,&n); Page: 1

2 for(i=0; i<n; i++) printf( \n Enter the details of employee:%d,i+1); printf( \n ID: ); scanf( %s,s[i].id); printf( \n Name: ); scanf( %s,s[i].name); printf( \n Salary: ); scanf( %s,&s[i].salary); printf( \n Details of the employees whose salary is more than 5000 ); for(i=0; i<n; i++) if(s[i].salary>5000) printf( \n ID: %s,s[i].id); printf( \n Name: %s,s[i].name); printf( \n Salary: %s,s[i].salary); return 0; 3. Explain Structure within a Structure with an example. A structure can be a member of another structure. This is called as nested structure. Example: Consider the structure as shown below: struct books char author[50]; char title[60]; char pubname[50]; char pubcity[40]; char pubstate[40]; int pubyear; ; The above structure can be written with nested structure as follows: Page: 2

3 We create another structure as below: struct pubinfo char name[50]; char city[40]; char state[40]; ; Now, we can rewrite the earlier structure as below: struct books char author[50]; char title[60]; struct pubinfo publisher ; int pubyear; ) book1; 4. What is a file? Explain fopen and fclose functions. A file is a collection data stored on the disk. An input file, also known as data file, contains items typed from keyboard. An output file contains the same information that can displayed on the screen. Syntax for fopen: fp=fopen(filename,mode); filename is the name of the disk file to be opened. mode defines the way file to be opened. Following are the different mode: r : the program will read from the file. w : the program will write to the file. a : the program will append new output to the end of the file. FILE *fpin,*fpout,*fpapp; fpin=fopen( rstud.dat, r ); fpout=fopen( wstud.out, w ); fpapp=fopen( astud, a ); Syntax for fclose(): fclose(filepointer); filepointer is the pointer to the file which has to be closed. Example: FILE *fpin,*fpout,*fpapp; fclose(fpin); fclose(fpout); fclose(fpapp); Page: 3

4 5. Explain fprintf and fscanf functions with syntax. Syntax for fprintf: fprintf (destfile, format string, list of variables); where the destfile is the name of the output stream(stdout or stderr) or a pointer to a file which has already opened. format string is used for formatting and list of variables are to be printed. FILE *fp; fp= fopen ( stud.dat, r ); if (fp==null) fprintf (stderr, Error in opening the file stud.dat\n ); exit(1); Syntax for fscanf: fscanf (sourcefile, format string, list of variables); where the sourcefile is the stdin or a pointer to a file which has already opened. format string is used for formatting and list of variables are to be scanned. FILE *fp; int num; fp= fopen( stud.dat, r ); fscanf(fp, %d,&num); 6. Explain fgets and fputs functions. Syntex for fgets(): This function takes three parameters and returns a value of the type char *. strptr=fgets(arrname, size, source) arrname is the name of the character array, size is an integer representing the size of the input, and source is the file from which to read. Syntax for fputs(): This function send the string to the output destination. fputs (sptr, destfile); sptr is pointer to a string destfile is output stream(stdout or stderr) or a pointer to a file. char line[80]; char *strptr; strptr=fgets(line,80,stdin); while (strptr!=null) ( fputs (strptr, stdout); strptr=fgets(line,80,stdin); Page: 4

5 7. What is a Structure data type? Give the general form of a Structure declaration. A structure is a collection of one or more data elements, possibly of different data types, grouped together under a single name. General form of structure declaration: struct structure_name Data_type element 1; Data_type element 2; Data_type element 3;.. Data_type element n; ; In the declaration keyword struct is followed by the name of the structure. The members should be enclosed between the braces. We can declare structure variable as follows: struct structrure_name var1,var2,,varn; Initialization of structure members: Struct structure_name var=value1, value2, valuen; 8. Using the Structure data type, write a program in C to read a student record from the keyboard and store it in a file called stud.dat. #include <stdio.h> struct student char id[10]; char name[20]; char branch[5]; ; int main() FILE *f; struct student s; f=fopen( stud.dat, w ); if(f==null) fprintf( stderr, \n Error in opening the file \n ); exit(1); printf( \n Enter 0 for ID to end the entry. ); Page: 5

6 while(1) prinff( \n ID : ); scanf( %d,s.id); if(strcmp(s.id, 0 )==0) break; printf( \ Name: ); scanf( %s,s.name); printf( \ Branch: ); scanf( %s,s.branch); //Write the entire structure to the file fwrite(&s, sizeof (struct student), 1,f); 9. Explain the differences between arrays and Structures. Arrays Structures 1. An array is a collection of data elements of 1. Structure is a collection of one or more the same type. data elements and the data elements can be of different data types. 2. Array behaves like a built in data types. 2. Structure is programmer defined data type. 3.Array allocates static memory. 3. Structure allocates dynamic memory 4.Array is a pointer to the first element. 4. Structure is not a pointer. 10. Write a program in C using Structure to read USN, name and marks in 3 subjects for each student and store it in a file called student.dat #include<stdio.h> #include<string.h> struct student char usn[10]; char name[30]; char math[3]; char phy[3]; char chem[3]; ; Page: 6

7 int main() FILE *f; struct student s; char c; f=fopen( student.dat, w ); if(f=null) fprintf( stderr, \nerror in opening the file ); exit(1); printf( \Enter student s details and enter 0 for USN to end ); while(1) printf( \n USN: ); scanf( %s,s.usn); if(strcmp(s.usn, 0 )==0) break; printf( \n Name: ); scanf( %s,s.name); printf( \n Mathematics: ); scanf( %d,s.math); printf( \n Physics: ); scanf( %d,s.chem); printf( \n Chemistry: ); scanf( %d,s.chem); //Write the entire structure to the file fwrite (&s, sizeof(struct student),1,f); fclose(f); return 0; 11. Explain file manipulation functions with example. fopen(): Create a new file or open existing file. fclose(): Closes a file. fscanf(): reads data from a file. fprintf(): wtites data to a file. Page: 7

8 fgets(): Reads string from file. fputs():writes to a file. 12. Explain array of Structure with an example. Structure is a collection of different data types which are grouped together. Array of structure is the collection of structures. struct student int id; char name[20]; char branch[10]; ; int main() int i; struct student record[2]; record[0].id=23; strcpy(record[0].name, Ronaldo ); strcpy(record[0].branch, CSE ); record[1].id=67; strcpy(record[0].name, Alex ); strcpy(record[0].branch, EEE ); for(i=0;i<2;i++) printf( \n ID=%d, record[i].id); printf( \n Name:%s,record[i].name); printf( \n Branch:%s,record[i].branch); 13. Write a C program to maintain a record of n student s details using an array of structure with four fields (rollno, name, marks and grade). Assume appropriate data type for each field. Print the student s information. #include<stdio.h> #include<string.h> Page: 8

9 struct student char rollno[10]; char name[30]; int mark; char grade[2]; ; int main() int i,n; struct student s[100]; printf( \n Enter the number of students (Maximum=100)); scanf( %d, &n); for(i=0; i<n; i++) printf( \n Roll No.: ); scanf( %s, &s[i].rollno); printf( \n Name: ); scanf( %s, &s[i].name); printf( \n Mark: ); scanf( %d, &s[i].mark); printf( \n Grade: ); scanf( %s, &s[i].grade); printf( \n Roll No.: ); scanf( %s, &s[i].rollno); for(i=0; i<n; i++) printf( \n Roll No.: %s,s[i].rollno); printf( \n Name: %s,s[i].name); printf( \n Mark: %d,s[i].mark); printf( \n Grade: %s,s[i].grade); return 0; 14. Explain various modes of FILE with example. Following are the different mode: r : the program will read from the file. w : the program will write to the file. a : the program will append new output to the end of the file. Page: 9

10 FILE *fpin,*fpout,*fpapp; fpin=fopen( rstud.dat, r ); fpout=fopen( wstud.out, w ); fpapp=fopen( astud, a ); Page: 10