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One-Dimensional Arrays
Introduction• A one-dimensional array is a sequence of homogenous elements stored in contigous memory
locations
• Motivating example: Suppose we need to store 100 scores in main memory.
//using simple variablesint x0, x1, x2, …, x99; x0 x1 … x99cin>>x0;cin>>x1;cin>>x2;…cin>>x99;
x[0] x[1] … x[99]//using arraysint x[100];for(int i=0; i<=99; i++) cin>>x[i];
Declaring One-Dimensional Arrays
• The general form of an array declaration
data_type array_name[expression]; • The data_type is the type of array elements. The array_name is a user defined identifier
(similar to variable name). The expression must evaluate to a positive integer and it cannot contain variables.
• Examplesint x[100] ; //x is an array of 100 integers (200 bytes)double z,w[50],u[30];char name[20], ch;
int n, m=5;#define k 5cin>>n;int d[n]; // compiler errorint d[m]; // compiler errorint d[k]; // ok
Array Initiliazation
• An array can be declared and initialized to some values
• Examplesint a[5]={2,3,1,1,0}; //valid a[0]=2, a[1]=3, a[2]=1, a[3]=1int b[5]={2}; //valid b[0] = 2, b[1] = 0, b[2] = 0int d[5]={1,2,3,4,5,6}; //compiler errorint c[ ]={1,3}; //validint e[ ]; // compiler error (unknown size)char f[3]={‘a’,’b’,’c’}; //validdouble h[2]={1.1,-1.7};
Using Array Elements
Array elements can be used wherever simple variables can be used. Examples:
int A[5]={2,5,12,4,0};A[2]++; //A[2] = A[2] + 1;cout<<A[2]; //13a[0]=a[1]+a[2]*3%a[3]; //if A array is used, 5 is displayedint I=4;A[I-1]=A[I];cout<<A[3];A[A[4]]++;cout<<A[A[4]]++; //3 displayed //cout<<A[3]>A[2];A[3]=A[2]=A[1]; //5I=2;if (A[I]>A[I-1]) //4 displayed cout<<A[I+1];else cout<<A[I-2];for(A[I]=0; A[I]>A[I+2]; I++) cout<<A[I]; //nothing displayed
Example: Given
float B[100]={ …};Write a code segment to print the values of B each element on a separate line.
int I;
for( I=0; I <=99; I++ )
cout<<B[I]<<endl;
Example: Given
float B[100]={ …};Write a code segment to print the values of B each two elements on a separate line.
int I;
for( I=0; I <=98; I+=2 )
cout<<B[I]<<“ ”<<B[I+1]<<endl;
Example: Given
float B[100]={ …};Write a code segment to print the values of B in reverse order.
int I;
for( I=99; I >=0; I-- )
cout<<B[I]<<endl;
Example: Given
float B[100]={ …};Write a code segment to count the number of negative values in B.
int I,count=0;
for( I=0; I <=99; I++ )
if (B[I]<0) count++;
cout<<count;
Example: Given double B[100]={ …};double C[100]={ …};double D[100];
Write a code segment to add B and C and store the result in D.
int I;
for( I=0; I <=99; I++ )
D[I]=B[I]+C[I];
Example: Given double B[100]={ …};double C[100]={ …};
Write a code segment to compute the dot product B.C
int I,result=0;
for( I=0; I <=99; I++ )
result+=B[I]*C[I];
Example: Given
long X[100]={ …};Write a code segment to print the maximum value in X.
int I, max;
for( max=X[0], I=1; I <=99; I++ )
if (X[I]>max) max=X[I];
cout<<max;
Example: Given
long X[100]={ …};Write a code segment to print the location of the maximum value in X.
int I, max, L;for( max=X[0],L=0, I=1; I <=99; I++ )
if (X[I]>max){ max=X[I]; L=I;}
printf(“the location is %d”,L);
Example: Given
long X[100]={ …};Write a code segment to count the number of values below average in X.
int I, sum, avg, count;for( I=0, sum=0; I <=99; I++ )
sum+=X[I];avg=sum/100;for( I=0, count=0; I <=99; I++ )
if (X[I]<avg) count++;printf(“the number of values =%d”,count);
Example: Given long X[100]={ …};
Write a code segment to test if elements in X are sorted.
int I;
for( I=0; I <=98 && X[I]<=X[I+1]; I++ );
if (I==99)
cout<<“sorted”;
else
cout<<“not sorted”;
Example: Given long X[100]={ …};long Y[100]={ …};
Write a code segment to test if X=Y.
int I;
for( I=0; I <=99 && X[I]==Y[I]; I++ );
if (I==100)
cout<<“equal”;
else
cout<<“not equal”;
Example: Given long X[100]={ …};
Write a code segment to reverse the values in X.
int I, Y[100];
for( I=0; I <=99; I++ ) Y[I]=X[99-I];
for( I=0; I <=99; I++ ) X[I]=Y[I];
Example: Givenint X[100]={ …};
Assume all values in X are between 0 and 19.Write a code segment to histogram the values in X
#include <iostream.h>void main(){int i,j;int a[100]={1,2,3,4,5,5,5,6,7,6,7,8,9,6,7,8,9,6, 7,8,9,0,0,0,1,1,1,3,3,5,2,1,1,1,1,4, 4,4,4,1,1,1,3,4,0,5,1,8,9,9,
11,12,3,14,15,15,15,16,17,16,17,18,19,6,7,8,9,6, 17,8,9,10,10,1,1,11,1,13,13,15,12,1,1,1,1,14, 14,4,4,1,11,1,13,14,10,5,1,18,9,19};
int count[20]={0};for(i=0; i<=99; i++) count[a[i]]++; //the value in the big array is the subscript in the
//small arrayfor(i=0; i<=19; i++){//to display the elements in the count array cout<<i<<” ”; for(j=1; j<=count[i]; j++) cout<<”*”;//to display stars count[i] times cout<<endl; } }
Example: Givenint X[100]={ …};
Write a code segment to compute the standard deviation of values in Xstandard deviation = √∑(xi – µ)2/n-1
int I, sum;double avg;for(I=0, sum=0; I<=99;I++) sum+=X[I];
avg=(double) sum/100;
for(I=0, sum=0; I<=99; I++) sum+=pow(X[I]-avg, 2);
cout<<sqrt(sum/99);
Example: Write a program to convert from decimal into binary
#include <iostream.h>
void main( ){
int num, I, count, A[1000];
cin>>num;
for (count=0; num ; num/=2) {
A[count]=num%2;
count++;
};
for(I=count-1; I>=0; I--) cout<<A[I];
}
Arrays of Characters
• One-dimensional arrays of characters are used to store names (strings). • Names stored in an array must terminate with NULL character. Also
represented as ‘\0’• The array
char N[4]; can store a name consisting of at most 3 characters.
• Arrays of characters can be declared and assigned strings in many ways: char N[4]=”Ali”; // stores the 4 characters ‘A’ ‘l’ ‘i’ NULL in array Nchar N[ ]=”Ali”; // defines an array of 4 elements and stores the 4
// characters ‘A’ ‘l’ ‘i’ and NULL in array Nchar N[4]={ ‘A’ , ‘l’ , ‘i’ , NULL}; // stores the 4 characters ‘A’ ‘l’
// ‘i’ NULL in array N• Extra Elements Are Filled Automatically With NULL
char N[4]={ ‘A’ , ‘l’ }; //Fills the last two elements with NULLchar N[5]={ ‘A’ , ‘h’,’m’,’a’,’d’ }; // Logical error: the string does not
// end with NULL
A L i \0
String Assigment and I/O
char N[10];
N=”ali”; //syntax errorN={‘A’ , ‘l’ , ‘i’ , NULL}; //syntax error
cin>>N; //ok
N[0]= ‘A’; N[1]= ‘l’; N[2]= ‘i’; N[3]= NULL; //okcout<<N; // prints Ali
cin>>N[0]; cin>>N[1]; cin>>N[2]; N[3]= NULL; //ok
char N[20]=”ahmad”;N[2]=NULL;cout<<N; // prints ah. cout keeps printing until NULL is reached.
Some Differences Between Character Arrays and Other Arrays
char N[10]={…};int A[5]={…};
cin >>N// okcin>>A// compiler error
cout<<N; //ok, prints the string in Ncout<<A; //Does not print the values in A
Write a program to read a string and print the number of characters in the string.
#include <iostream.h>
void main(){
int i;
char N[20];
cin>>N;
for(i=0; N[i]; i++);
cout<<i;
}
Write a program to read a string and print the last character in the string.
#include <iostream.h>
void main(){
int i;
char N[20];
cin>>N;
for(i=0; N[i]; i++);
cout<<N[i-1];
}
Write a program to read a string and delete the last (not NULL) character in the string.
#include <iostream.h>
void main(){
int i;
char N[20];
cin>>N;
for(i=0; N[i]; i++);
N[i-1]=NULL;
}
Write a program to read a string and print the characters of the string each on a separate line.
#include <iostream.h>
void main(){
int i;
char N[20];
cin>>N;
for(i=0; N[i]; i++)
cout<<N[i]<<endl;
}
Write a program to read a string and print it in reverse order.
#include <iostream.h>
void main(){
int i;
char N[20];
cin>>N;
for(i=0; N[i]; i++);
for(int j=i-1; j>=0; j--)
cout<<N[j];
}
Example: Givenchar X[100]={ …};
Write a code segment to capitalize every character in the string X
for(int i=0; X[i]; i++)
if(X[i]>=‘a’ &&X[i]<=‘z’)
X[i]=X[i]-’a’+’A’;
Example: Givenchar X[100]= … ;char Y[100]= … ;
Write a code segment to append the string Y at end of X.
int i;
for(i=0; X[i]; i++);
for(int j=0; Y[j]; i++, j++) X[i]=Y[j];
X[i]=NULL;
Example: Write a program to read a string consisting of small letters and print the number of occurrences of each letter a..z in this string.
#include <iostream.h>void main(){
int i,count[26]={0};char name[20];cout<<”Enter Name:”;cin>>name;for(i=0; name[i]!=NULL; i++)
count[name[i]-‘a’]++;
for(i=0; i<=25; i++) cout<<endl<<”count(”<<(char) (‘a’+i)<<”)=”<<count[i]; }
Example: Write a program to read a string consisting of small letters and print the number of occurrences of each letter a..z in this string.
#include <iostream.h>void main(){
int i,count[26]={0};char name[20];cout<<”Enter Name:”;cin>>name;for(i=0; name[i]!=NULL; i++)
count[name[i]-‘a’]++;
for(i=0; i<=25; i++) cout<<endl<<”count(”<<(char) (‘a’+i)<<”)=”<<count[i]; }
Example: Write a program to read 10 names and find the number of names starting with a.
#include <iostream.h>void main(){
char name[20];int i, count=0;for(i=1; i<=10; i++){
cin>>name;if (name[0]=='a') count++;
}cout<<endl<<"Number of names starting with a ="<<count;
}
Example: Write a program that reads 20 strings and finds the length of the shortest string .
#include <iostream.h>void main(){
char name[20];int shortestLength=1000, j ,i;for(i=1; i<=20; i++){
cin>>name;for(j=0; name[j]; j++);if(j<shortestLength) shortestLength=j;
}cout<<endl<<“shortest string length is "<<shortestLength;
}
Example:Write a program to determine the location of a character in a string (if it occurs) .
#include <iostream.h>void main(){
char name[20], ch;int i;cin>>name;cin>>ch;for(i=0; name[i]!=ch && name[i]!=NULL ; i++);if (name[i]==ch)
cout<<“Location=”<<i;else
cout<<ch<<“does not exist in ”<<name;}
Example:Write a program to determine the location of a substring in a string (if it occurs) .
#include <iostream.h>void main(){
char S1[20], S2[20];int I, J, flag=1;cout<<“input string”;cin>>S1;cout<<“input sustring”;cin>>S2;for(i=0; s1[i] && flag; i++){
int k=i;for(j=0; S2[j]&&S2[j]==S1[k]; j++,k++);if (S2[j]==NULL) flag=0;
}if (flag==0)
cout<<“Location=”<<i;else
cout<<S2 <<“ does not exist in ”<<S1;}
Parallel Arrays
• Information about an object can be distributed over a number of one-dimentional arrays.
• Example: Information about students can be distributed over several arrays.
int student_id[50]={10432187, … };
int exam1[50]={70, … };
int exam2[50]={72, … };
int final_exam[50]= {68, … };
Example: Givenint student_id[50]={10432187, … };int exam1[50]={70, … };int exam2[50]={72, … };int final_exam[50]= {68, … };
Write a code segment to compute the final grades of the students. Assume exam1 and exam2 has 25% each and the final exam has 50%.
double G;for(int i=0; i<=49; i++){
G=0.25*exam1[i]+0.25*exam2[i]+ 0.5*final_exam[i];cout<<endl<<student_id[i]<<“
”<<G; }
Example: Givenint student_id[50]={10432187, … };int exam1[50]={70, … };int exam2[50]={72, … };int final_exam[50]= {68, … };
Write a code segment to print the scores of a student given the ID .
int N;
cin>>N;
for(int i=0; i<=49 &&student_id[i]!=N; i++);
if (i==50)
cout<<“student id does not exist”;
else
cout<<exam1[i]<<exam2[i]<<final_exam[i];
Example: Givenint student_id[50]={10432187, … };int exam1[50]={70, … };int exam2[50]={72, … };int final_exam[50]= {68, … };
Write a code segment to count the number of students passing in the first exam and failing in the second exam .
int count=0;
for(int i=0; i<=49; i++)
if (exam1[i]>=60 && exam2[i]<60)
count++;
cout<<count;
Example: Givenint student_id[50]={10432187, … };int exam1[50]={70, … };int exam2[50]={72, … };int final_exam[50]= {68, … };
Write a code segment to print the ID of the student having the maximum score in the first exam.
int max, L;for(int i=0, max=exam2[0], L=0; i<=49; i++)
if (exam2[i]>max){max=exam2[i];L=I;
};cout<<student_id[L];
Example: Givenint student_id[50]={10432187, … };int exam1[50]={70, … };int exam2[50]={72, … };int final_exam[50]= {68, … };
Write a code segment to find which of the 3 exams has the highest number of passing students.
int count1=0, count2=0, count3=0, i;for(i=0; i<=49; i++) if (exam1[i]>=60)count1++;for(i=0; i<=49; i++) if (exam2[i]>=60)count2++;for(i=0; i<=49; i++) if (final_exam1[i]>=60)count3++;if (count1>=count2)
if(count1>=count3)cout<<“exam1”;
elsecout<<“exam3”;
elseif (count2>=count3)
cout<<“exam2”;else
cout<<“exam3”;
