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One-Dimensional Arrays

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 variables int x0, x1, x2, …, x99; x0 x1 … x99

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One-Dimensional Arrays

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  1. One-Dimensional Arrays

  2. 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 variables int x0, x1, x2, …, x99; x0 x1 … x99 cin>>x0; cin>>x1; cin>>x2; … cin>>x99; x[0] x[1] … x[99] //using arrays int x[100]; for(int i=0; i<=99; i++) cin>>x[i];

  3. Declaring One-Dimensional Arrays • The general form of an array declaration data_typearray_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. • Examples int 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 5 cin>>n; int d[n]; // compiler error int d[m]; // compiler error int d[k]; // ok

  4. Array Initiliazation • An array can be declared and initialized to some values • Examples int a[5]={2,3,1,1,0}; //valid a[0]=2, a[1]=3, a[2]=1, a[3]=1 int b[5]={2}; //valid b[0] = 2, b[1] = 0, b[2] = 0 int d[5]={1,2,3,4,5,6}; //compiler error int c[ ]={1,3}; //valid int e[ ]; // compiler error (unknown size) char f[3]={‘a’,’b’,’c’}; //valid double h[2]={1.1,-1.7};

  5. 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]; //13 a[0]=a[1]+a[2]*3%a[3]; //if A array is used, 5 is displayed int 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]; //5 I=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

  6. 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;

  7. 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;

  8. 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;

  9. 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;

  10. 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];

  11. 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];

  12. 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;

  13. 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);

  14. 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);

  15. 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”;

  16. 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”;

  17. 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];

  18. Example: Given int 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 array for(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; } }

  19. Example: Given int 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);

  20. 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]; }

  21. 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 N char N[ ]=”Ali”; // defines an array of 4 elements and stores the 4 // characters ‘A’ ‘l’ ‘i’ and NULL in array N char 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 NULL char N[5]={ ‘A’ , ‘h’,’m’,’a’,’d’ }; // Logical error: the string does not // end with NULL

  22. String Assigment and I/O char N[10]; N=”ali”; //syntax error N={‘A’ , ‘l’ , ‘i’ , NULL}; //syntax error cin>>N; //ok N[0]= ‘A’; N[1]= ‘l’; N[2]= ‘i’; N[3]= NULL; //ok cout<<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.

  23. Some Differences Between Character Arrays and Other Arrays char N[10]={…}; int A[5]={…}; cin >>N// ok cin>>A// compiler error cout<<N; //ok, prints the string in N cout<<A; //Does not print the values in A

  24. 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; }

  25. 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]; }

  26. 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; }

  27. 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; }

  28. 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]; }

  29. Example: Given char 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’;

  30. Example: Given char 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;

  31. 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]; }

  32. 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]; }

  33. 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; }

  34. 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; }

  35. 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; }

  36. 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; }

  37. 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, … };

  38. Example: Given int 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; }

  39. Example: Given int 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];

  40. Example: Given int 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;

  41. Example: Given int 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];

  42. Example: Given int 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”; else cout<<“exam3”; else if (count2>=count3) cout<<“exam2”; else cout<<“exam3”;

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