printf() and scanf() format
printf("%d", n);
FORMAT ARGUMENT TYPE
%d, %i int decimal
%u unsigned int
%x unsigned int hexadecimal
%#x unsigned int hexadecimal with prefix 0x
%f double
%Lf long double
%e, %E double scientific notation
%c int to print a character
%s char * string (character array ended with '\0')
%p void * print memory address
%g, %G double %f or %e depending on the length
scanf("%d", &n);
FORMAT ARGUMENT TYPE
%d int * &n, store the input integer in n
%ld long *
%lld long long *
%u unsigned int *
%f float * read float
%lf double * read double
%Lf long double * read long double
%c char * read 3 characters %3c
%s char * read a string until whitespace
%n int * with %s, to get string length
char a[100]; int len;
scanf("%s%n", a, &len);
len will have the string length
Frequently used functions
#include <string.h>
char str[10];
scanf("%s", str);
to get the string length using strlen(str)
#include <ctype.h>
isspace(ch), islower(ch), isupper(ch), isdigit(ch)
isalpha(ch), toupper(ch), tolower(ch)
To create a 5-by-5 two-dimensional array, we need to write
int a[5][5];
It will be indexed as follows:
|
a[0][0] |
a[0][1] |
a[0][2] |
a[0][3] |
a[0][4] |
|
a[1][0] |
a[1][1] |
a[1][2] |
a[1][3] |
a[1][4] |
|
a[2][0] |
a[2][1] |
a[2][2] |
a[2][3] |
a[2][4] |
|
a[3][0] |
a[3][1] |
a[3][2] |
a[3][3] |
a[3][4] |
|
a[4][0] |
a[4][1] |
a[4][2] |
a[4][3] |
a[4][4] |
How to read the following data?
1 2 3 4 5 e
#include <stdio.h>
int main(void)
{
int x;
while (scanf("%d", &x) == 1) {
printf("x=%d\n", x);
}
return 0;
}
How to read the following data?
2
L 5 2
D 5 3
#include <stdio.h>
int main(void)
{
char ch;
int i, n, row, col;
scanf("%d", &n);
for (i=0; i<n; i++) {
while(getchar()!='\n');
scanf("%c%d%d", &ch, &row, &col);
}
return 0;
}
Using for loops to print a two-dimensional array
for(i = 0; i < row; i++) {
for (j = 0; j < col; j++) {
printf("%5d", A[i][j]);
}
printf("\n");
}
Using bubble sort to rearrange an array A
for (i = 0; i < n; i++) {
for (j = 1; j < n; j++) {
if (A[j] > A[j-1]) {
/* swap A[j] A[j-1] */
}
}
}
operators:
! && || == != + - * / %
> < >= <=
How to avoid common errors and how to debug for OJ
1. Put the arrays in the 'global' area. Set their size bigger than required. Avoid using variable-length arrays (e.g. int arr[n];). Keep the array size fix (e.g., int arr[1000];).
2. After writing the code for reading input data, you may print out the data to check if your code reads them correctly. Do not proceed to write subsequent code before you confirm that.
3. If your program crashes, usually it is caused by memory related errors. Check the ranges of for-loops to see if your code attempts to read or write the elements out of the arrays’ boundary.
#include <string.h>
strstr(str1,str2)
return a pointer to the first occurrence in str1 of the entire sequence of characters specified in str2, or a null pointer if the sequence is not present in str1.
strcmp(str1,str2)
Compare two strings.
return
|
|
if the first character that does not match has a lower value in ptr1 than in ptr2 |
|
|
if the contents of both strings are equal |
|
|
if the first character that does not match has a greater value in ptr1 than in ptr2 |
strncmp(str1,str2,num)
Compares up to num characters of the C string str1 to those of the C string str2
return
|
|
if the first character that does not match has a lower value in str1 than in str2 |
|
|
if the contents of both strings are equal |
|
|
if the first character that does not match has a greater value in str1 than in str2 |
#include <stdlib.h>
malloc(size)
return a pointer to the memory block allocated by the function.